Management of electrical stimulation therapy

ABSTRACT

The techniques of the disclosure describe example medical devices, systems, and methods for delivering electrical stimulation therapy to a patient. In one example, a medical device selects subsets of a plurality of therapy parameter sets that define electrical stimulation therapy, each subset including at least one therapy parameter set and less than all of the therapy parameter sets. Further, the medical device delivers, via a plurality of electrodes, electrical stimulation therapy according to each subset via a respective set of electrodes different from sets of electrodes of each other subset of the therapy parameter sets. The medical device iteratively delivers the electrical stimulation therapy according to the subsets of the therapy parameter sets via the respective sets of electrodes. Further, the medical device selects at least one subset of the therapy parameter sets that treat a condition of the patient for defining subsequent delivery of electrical stimulation to the patient.

This application claims the benefit of U.S. Provisional Application No.62/570,510 by Torgerson, entitled “MANAGEMENT OF ELECTRICAL STIMULATIONTHERAPY,” and filed on Oct. 10, 2017. The entire content of ApplicationNo. 62/570,510 is incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to electrical stimulation therapy,and, more specifically, selection of stimulation parameters that defineelectrical stimulation therapy.

BACKGROUND

Medical devices may be external or implanted, and may be used to deliverelectrical stimulation therapy to patients to various tissue sites totreat a variety of symptoms or conditions such as chronic pain, tremor,Parkinson's disease, epilepsy, urinary or fecal incontinence, sexualdysfunction, obesity, or gastroparesis. A medical device may deliverelectrical stimulation therapy via one or more leads that includeelectrodes located proximate to target locations associated with thebrain, the spinal cord, pelvic nerves, peripheral nerves, or thegastrointestinal tract of a patient. Hence, electrical stimulation maybe used in different therapeutic applications, such as deep brainstimulation (DBS), spinal cord stimulation (SCS), pelvic stimulation,gastric stimulation, or peripheral nerve field stimulation (PNFS).

A clinician may select values for a number of programmable parameters inorder to define the electrical stimulation therapy to be delivered bythe implantable stimulator to a patient. For example, the clinician mayselect one or more electrodes, a polarity of each selected electrode, avoltage or current amplitude, a pulse width, and a pulse frequency asstimulation parameters. A set of parameters, such as a set includingelectrode combination, electrode polarity, amplitude, pulse width andpulse rate, may be referred to as a program in the sense that theydefine the electrical stimulation therapy to be delivered to thepatient. Such a set of parameters may be referred to herein as an“electrical stimulation therapy parameter set” or “therapy parameterset.”

SUMMARY

In general, the disclosure describes example medical devices, systems,and techniques for delivering a plurality of electrical stimulationtherapy programs to a patient via a plurality of electrode combinationsfrom an implantable medical device (IMD), e.g., simultaneously or on atime-interleaved basis. An IMD may deliver electrical stimulation to aplurality of target tissue areas over a portion of the body of thepatient via respective electrode combinations to evaluate efficacy ofthe electrical stimulation for treating a condition of the patient. Forexample, the electrical stimulation may be configured to suppress one ormore symptoms of a disease of the patient (e.g., pain or unwantedsensations). By delivering the electrical stimulation to the pluralityof target tissue areas, a clinician may rapidly determine whether theelectrical stimulation therapy can be effective for treating the patient(e.g., suppressing one or more symptoms of a disease of the patient)without separately delivering the electrical stimulation to each targettissue area before determining stimulation efficacy.

After determining whether the electrical stimulation is effective fortreating the patient, the IMD may separately deliver the electricalstimulation to subsets of the plurality of target tissue areas todetermine whether any of the subset of the target tissue areas providesefficacious treatment to the patient. For example, a programmer or theIMD may remove at least one electrode or at least one pair of electrodes(e.g., from the plurality of electrodes used in the electrodecombinations that treated each respective target tissue area) such thatat least one of the target tissue areas of the plurality of targettissue areas does not receive electrical stimulation. The clinicianand/or patient may then evaluate which of these tissue area subsetsmaintain efficacious therapy. In this fashion, the techniques of thedisclosure may determine a primary set of electrodes that deliverselectrical stimulation therapy to a tissue area smaller than thecollective plurality of target tissue areas while maintaining effectivetherapy. In turn, the IMD may conserve energy by delivering electricalstimulation therapy via the primary set of electrodes to this smallertissue area. Such techniques may reduce the power usage required todeliver the electrical stimulation therapy over time while maintainingthe desired therapy initially provided by delivery electricalstimulation to the plurality of target tissue areas.

In one example, this disclosure describes a method comprising:delivering, by a medical device via a plurality of electrodes,electrical stimulation therapy according to a plurality of therapyparameter sets to a plurality of respective tissue sites of a patient,the electrical stimulation therapy treating a condition of the patient;subsequent to delivering the electrical stimulation therapy according tothe plurality of therapy parameter sets, selecting a plurality ofsubsets of the plurality of therapy parameter sets, wherein each subsetof the plurality of therapy parameter sets includes at least one therapyparameter set of the plurality of therapy parameter sets and less thanall of the plurality of therapy parameter sets, and wherein electricalstimulation therapy is delivered according to each subset of theplurality of therapy parameter sets via a respective set of electrodesdifferent from sets of electrodes that deliver other subsets of theplurality of therapy parameter sets; iteratively delivering, by themedical device, electrical stimulation therapy according to the subsetsof the plurality of therapy parameter sets to the patient via therespective sets of electrodes; receiving, for each of the subsets of theplurality of therapy parameter sets, feedback from the patientindicating whether the subset of the plurality of therapy parameter setstreated the condition of the patient; and selecting, based on thefeedback from the patient, at least one subset of the plurality oftherapy parameter sets that treat the condition of the patient fordefining subsequent delivery of electrical stimulation therapy to thepatient.

In another example, this disclosure describes a medical device systemcomprising: stimulation circuitry of a medical device configured todeliver, via a plurality of electrodes, electrical stimulation therapyaccording to a plurality of therapy parameter sets to a plurality ofrespective tissue sites of a patient, the electrical stimulation therapytreating a condition of the patient; and processing circuitry configuredto: subsequent to delivering electrical stimulation therapy according tothe plurality of therapy parameter sets, select a plurality of subsetsof the plurality of therapy parameter sets, wherein each subset of theplurality of therapy parameter sets includes at least one therapyparameter set of the plurality of therapy parameter sets and less thanall of the plurality of therapy parameter sets, and wherein electricalstimulation therapy is delivered according to each subset of theplurality of therapy parameter sets via a respective set of electrodesdifferent from sets of electrodes that deliver other subsets of theplurality of therapy parameter sets; iteratively control delivery, bythe stimulation circuitry of the medical device, of electricalstimulation therapy according to the subsets of the plurality of therapyparameter sets to the patient via the respective sets of electrodes;receive, for each of the subsets of the plurality of therapy parametersets, feedback from the patient indicating whether the subset of theplurality of therapy parameter sets treated the condition of thepatient; and select, based on the feedback from the patient, at leastone subset of the plurality of therapy parameter sets that treat thecondition of the patient for defining subsequent delivery of electricalstimulation therapy to the patient.

In another example, this disclosure describes a medical device systemcomprising: means for delivering, via a plurality of electrodes,electrical stimulation therapy according to a plurality of therapyparameter sets to a plurality of respective tissue sites of a patient,the electrical stimulation therapy treating a condition of the patient;means for, subsequent to delivering the electrical stimulation therapyaccording to the plurality of therapy parameter sets, selecting aplurality of subsets of the plurality of therapy parameter sets, whereineach subset of the plurality of therapy parameter sets includes at leastone therapy parameter set of the plurality of therapy parameter sets andless than all of the plurality of therapy parameter sets, and whereinelectrical stimulation therapy is delivered according to each subset ofthe plurality of therapy parameter sets via a respective set ofelectrodes different from sets of electrodes that deliver other subsetsof the plurality of therapy parameter sets; means for iterativelydelivering electrical stimulation therapy according to the subsets ofthe plurality of therapy parameter sets to the patient via therespective sets of electrodes; means for receiving, for each of thesubsets of the plurality of therapy parameter sets, feedback from thepatient indicating whether the subset of the plurality of therapyparameter sets treated the condition of the patient; and means forselecting, based on the feedback from the patient, at least one subsetof the plurality of therapy parameter sets that treat the condition ofthe patient for defining subsequent delivery of electrical stimulationtherapy to the patient.

The details of one or more examples of the techniques of this disclosureare set forth in the accompanying drawings and the description below.Other features, objects, and advantages of the techniques will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example system thatincludes a medical device programmer and an implantable medical device(IMD) configured to deliver electrical stimulation therapy to a patient.

FIG. 2 is a block diagram of the example IMD of FIG. 1.

FIG. 3 is a block diagram of the example external programmer of FIG. 1.

FIG. 4 is an illustration depicting an example user interface for anexternal programmer of FIG. 1.

FIGS. 5A-5B are illustrations depicting example electrode leads of theIMD of FIG. 1.

FIG. 6 is a flowchart illustrating an example operation according to thetechniques of the disclosure.

FIG. 7 is a flowchart illustrating an example operation according to thetechniques of the disclosure.

FIG. 8 is a flowchart illustrating an example operation according to thetechniques of the disclosure.

DETAILED DESCRIPTION

An implantable medical device may deliver electrical stimulation therapyto treat a condition of a patient. High-frequency electrical stimulation(e.g., electrical stimulation having pulses of a frequency greater thanor equal to 1,000 Hertz) can be effective at treating conditions such aspain during SCS. For example, when treating chronic pain in a patient,low-frequency electrical stimulation may induce paresthesia in thepatient, which masks the sensation of pain, but the sensation ofparesthesia itself may be uncomfortable to the patient. In contrast,high-frequency electrical stimulation may suppress pain in the patientwithout substantially producing paresthesia (e.g., without causingperceptible sensations of paresthesia in the patient). Furthermore,increasing the frequency of the electrical stimulation therapy beyond1,000 Hertz, or some other similar threshold for a patient) may notprovide any additional benefit in treating the condition of the patientand also may not be perceived any differently by the patient.

The efficacy of the electrical stimulation may be related to one or moreparameters of the electrical stimulation, such as the frequency of theelectrical stimulation, as described above, as well as the pulse widthof the electrical stimulation, one of current amplitude or voltageamplitude of the electrical stimulation, a combination of electrodes,etc. Furthermore, the efficacy of the electrical stimulation therapy maydepend on the placement of individual electrodes disposed along one ormore leads of the IMD relative to a spinal cord of the patient.Therefore, after a procedure in which a lead and/or an BID is implantedwithin a patient, a clinician may test, in a clinic or an outpatientsetting, electrical stimulation therapy defined by various electricalstimulation therapy parameter sets to determine an electricalstimulation therapy that effectively treats a condition of the patient.This period may be referred to as a trial period. As one example, theclinician may test various combinations of electrodes and differentelectrical stimulation therapy parameters, etc., to determine anelectrical stimulation therapy that effectively suppresses one or moresymptoms of a disease of the patient, such as chronic pain. In oneexample, such an outpatient evaluation may occur during an evaluationtrial of about 10 days. However, during this trial, the patient mayrequire several days to demonstrate a response to any particularelectrical stimulation therapy program, such as paresthesia, painrelief, or the suppression of the one or more symptoms of the disease.Therefore, if the clinician were to test only a single electricalstimulation therapy at a time (e.g., a single electrode combination andlocation of the electrical stimulation therapy), he or she would beunable to test more than two or three different electrical stimulationtherapy programs before the outpatient evaluation ends. Since there arelikely many more options for therapy, the clinician may not have enoughtime to identify an electrical stimulation therapy program thateffectively treats the condition of the patient. For example, in thislimited trial period, the clinician may be unable to try all possibleelectrode combinations (e.g., deliver electrical stimulation to allpossible tissue areas of the patient) to determine if an electricalstimulation program exists that is effective in treating the conditionof the patient. Thus, upon individually testing only a fewhigh-frequency electrical stimulation therapy programs that do notresult in effective treatment of the condition of the patient, theclinician may need to choose an alternative therapy that may be lesseffective or determine that the patient is not a candidate forelectrical stimulation therapy.

As described herein, a medical system is configured to deliver, via aplurality of electrode combinations of electrodes disposed along a leadof an IMD, a plurality of electrical stimulation therapy programs to thepatient. In some examples, the IMD delivers each of the plurality ofelectrical stimulation therapy programs on a time-interleaved basis withone another, while in other examples, the IMD delivers each of theplurality of electrical stimulation therapy programs substantiallysimultaneously. In some examples where each of the plurality ofelectrical stimulation therapy programs on a time-interleaved basis withone another, each electrical stimulation therapy program may comprise asingle electrical stimulation pulse. In either simultaneous deliver ortime-interleaved delivery, the patient may perceive the effects of theplurality of electrical stimulation therapy programs at the same time.Furthermore, such electrical stimulation is delivered to a plurality oftarget tissue areas over a large portion of the spinal cord of thepatient. By ensuring maximal coverage of the spinal cord, the clinicianmay quickly determine (e.g., within a trial period such as a trialperiod of about 3 days) whether the electrical stimulation therapy iscapable of treating the condition of the patient. In this fashion, thetechniques of the disclosure may allow for the rapid determination ofwhether electrical stimulation therapy is effective for treating acondition of patient. Furthermore, after determining whether theelectrical stimulation is effective for treating the condition of thepatient, the system may iteratively deliver electrical stimulation viasubsets of electrodes to subsets of target tissue areas. In thisfashion, the system may determine a primary set of electrodes thatdelivers electrical stimulation therapy to a tissue area smaller thanthe collective plurality of target tissue areas of the spinal cord ofthe patient while maintaining effective therapy. This reduction inelectrodes, or therapy parameter sets, may allow the IMD to conserveenergy by delivering electrical stimulation only via the primary set ofelectrodes to this smaller tissue area. This primary set of electrodesmay be from one or more of the electrical stimulation therapy parametersets tested with the plurality of electrical stimulation therapyparameter sets. Such techniques may reduce the power usage required todeliver the electrical stimulation over time while maintaining thedesired therapy initially provided by delivery of the electricalstimulation therapy to the plurality of target tissue areas.

FIG. 1 is a conceptual diagram illustrating example system 100 thatincludes medical device programmer 104 and implantable medical device(IMD) 102 configured to deliver electrical stimulation therapy topatient 12. In the example shown in FIG. 1, IMD 102 is configured todeliver SCS therapy. Although the techniques described in thisdisclosure are generally applicable to a variety of medical devicesincluding external and implantable medical devices (IMDs), applicationof such techniques to IMDs and, more particularly, implantableelectrical stimulators (e.g., neurostimulators) will be described forpurposes of illustration. More particularly, the disclosure will referto an implantable spinal cord stimulation (SCS) system for purposes ofillustration, but without limitation as to other types of medicaldevices or other therapeutic applications of medical devices.

As shown in FIG. 1, system 100 includes an IMD 102, leads 16A, 16B, andexternal programmer 104 shown in conjunction with a patient 12, who isordinarily a human patient. In the example of FIG. 1, IMD 102 is animplantable electrical stimulator that is configured to generate anddeliver electrical stimulation therapy to patient 12 via electrodes ofleads 16A, 16B, e.g., to treat symptoms of a condition such as relieffrom chronic pain or other symptoms. IMD 102 may be a chronic electricalstimulator that remains implanted within patient 12 for weeks, months,or even years. In other examples, IMD 102 may be a temporary, or trial,stimulator used to screen or evaluate the efficacy of electricalstimulation for chronic therapy. In one example, IMD 102 is implantedwithin patient 12, while in another example, IMD 102 is an externaldevice coupled to percutaneously implanted leads. In some examples, IMDuses one or more leads, while in other examples, IMD 102 is leadless. Insome examples, leads 16A, 16B may be percutaneous leads for trialstimulation, chronic implanted leads, or include a display chronicimplanted portion that carries the electrodes coupled to a leadextension that remains implanted within the patient and coupled to animplanted DAD 102 or coupled to a percutaneous lead extension that iscoupled to an external IMD 102. In this manner, leads 16A, 16B may beused during a trial process with an external IMD and retained for uselater with an implanted IMD.

IMD 102 may be constructed of any polymer, metal, or composite materialsufficient to house the components of IMD 102 (e.g., componentsillustrated in FIG. 2) within patient 12. In this example, IMD 102 maybe constructed with a biocompatible housing, such as titanium orstainless steel, or a polymeric material such as silicone, polyurethane,or a liquid crystal polymer, and surgically implanted at a site inpatient 12 near the pelvis, abdomen, or buttocks. In other examples, IMD102 may be implanted within other suitable sites within patient 12,which may depend, for example, on the target site within patient 12 forthe delivery of electrical stimulation therapy. The outer housing of IMD102 may be configured to provide a hermetic seal for components, such asa rechargeable or non-rechargeable power source. In addition, in someexamples, the outer housing of IMD 102 may be selected from a materialthat facilitates receiving energy to charge the rechargeable powersource.

Electrical stimulation energy, which may be constant current or constantvoltage based pulses, for example, is delivered from IMD 102 to one ormore target tissue sites of patient 12 via one or more electrodes (notshown) of implantable leads 16A and 16B (collectively “leads 16”). Inthe example of FIG. 1, leads 16 carry electrodes that are placedadjacent to the target tissue of spinal cord 20. One or more of theelectrodes may be disposed at a distal tip of a lead 16 and/or at otherpositions at intermediate points along the lead. Leads 16 may beimplanted and coupled to IMD 102. The electrodes may transfer electricalstimulation generated by an electrical stimulation generator in IMD 102to tissue of patient 12. Although leads 16 may each be a single lead,lead 16 may include a lead extension or other segments that may aid inimplantation or positioning of lead 16. In some other examples, IMD 102may be a leadless stimulator with one or more arrays of electrodesarranged on a housing of the stimulator rather than leads that extendfrom the housing. In addition, in some other examples, system 100 mayinclude one lead or more than two leads, each coupled to IMD 102 anddirected to similar or different target tissue sites.

The electrodes of leads 16 may be electrode pads on a paddle lead,circular (e.g., ring) electrodes surrounding the body of the lead,conformable electrodes, cuff electrodes, segmented electrodes (e.g.,electrodes disposed at different circumferential positions around thelead instead of a continuous ring electrode), or any other type ofelectrodes capable of forming unipolar, bipolar or multipolar electrodecombinations for therapy. Ring electrodes arranged at different axialpositions at the distal ends of lead 16 will be described for purposesof illustration.

The deployment of electrodes via leads 16 is described for purposes ofillustration, but arrays of electrodes may be deployed in differentways. For example, a housing associated with a leadless stimulator maycarry arrays of electrodes, e.g., rows and/or columns (or otherpatterns), to which shifting operations may be applied. Such electrodesmay be arranged as surface electrodes, ring electrodes, or protrusions.As a further alternative, electrode arrays may be formed by rows and/orcolumns of electrodes on one or more paddle leads, In some examples,electrode arrays may include electrode segments, which may be arrangedat respective positions around a periphery of a lead, e.g., arranged inthe form of one or more segmented rings around a circumference of acylindrical lead.

Electrical stimulation therapy is defined by a set of therapy parameters(e.g., a set of electrical stimulation parameters) that may also bereferred to as a therapy program. The set of electrical stimulationparameters define deliver of stimulation therapy by IMD 102 through theelectrodes of leads 16. The electrical stimulation parameters mayinclude information identifying which electrodes have been selected fordelivery of stimulation, the polarities of the selected electrodes,i.e., the electrode combination for the program, and voltage or currentamplitude, pulse rate, and pulse width of electrical pulses delivered bythe electrodes. Delivery of stimulation pulses will be described forpurposes of illustration, but the electrical stimulation parameters maydefine other signals such as sine waves, triangle waves, square waves,or other types of electrical signals.

Although FIG. 1 is directed to SCS therapy, e.g., used to treat pain, inother examples system 100 may be configured to treat any other conditionthat may benefit from electrical stimulation therapy. For example,system 100 may be used to treat tremor, Parkinson's disease, epilepsy, apelvic floor disorder (e.g., urinary incontinence or other bladderdysfunction, fecal incontinence, pelvic pain, bowel dysfunction, orsexual dysfunction), obesity, gastroparesis, or psychiatric disorders(e.g., depression, mania, obsessive compulsive disorder, anxietydisorders, and the like). In this manner, system 100 may be configuredto provide therapy taking the form of deep brain stimulation (DBS),peripheral nerve stimulation (PNS), peripheral nerve field stimulation(PNFS), cortical stimulation (CS), pelvic floor stimulation,gastrointestinal stimulation, or any other stimulation therapy capableof treating a condition of patient 12.

In some examples, lead 16 may include one or more sensors configured toallow IMD 102 to monitor one or more parameters of patient 12. The oneor more sensors may be provided in addition to, or in place of, therapydelivery by lead 16.

IMD 102 is configured to deliver electrical stimulation therapy topatient 12 via selected combinations of electrodes carried by one orboth of leads 16, alone or in combination with an electrode carried byor defined by an outer housing of IMD 102. The target tissue for theelectrical stimulation therapy may be any tissue affected by electricalstimulation, which may be in the form of electrical stimulation pulsesor continuous waveforms. In some examples, the target tissue includesnerves, smooth muscle, or skeletal muscle. In the example illustrated byFIG. 1, the target tissue is tissue proximate spinal cord 20, such aswithin an intrathecal space or epidural space of spinal cord 20, or, insome examples, adjacent nerves that branch off of spinal cord 20. Leads16 may be introduced into spinal cord 20 in via any suitable region,such as the thoracic, cervical, or lumbar regions. Stimulation of spinalcord 20 may, for example, prevent pain signals from traveling throughspinal cord 20 and to the brain of patient 12. Patient 12 may perceivethe interruption of pain signals as a reduction in pain and, therefore,efficacious therapy that treats a condition of the patient 12.

IMD 102 is configured to generate and deliver electrical stimulationtherapy to a target stimulation site within patient 12 via theelectrodes of leads 16 to patient 12 according to one or more therapyprograms. A therapy program defines values for one or more electricalparameters that define an aspect of the therapy delivered by IMD 102according to that program defining the electrical parameter values. Forexample, a therapy program that defines delivery of stimulation by IMD102 in the form of pulses may define values for voltage or current pulseamplitude, pulse width, and pulse rate for stimulation pulses deliveredby IMD 102.

Moreover, in some examples, IMD 102 delivers electrical stimulationtherapy to patient 12 according to multiple therapy programs, which maybe stored as a therapy program group. For example, as described below,in some examples, IMD 102 may deliver different pulses of electricalstimulation signal via respective electrode combinations, and each ofthe electrode combinations may be associated with a respective therapyprogram. The therapy programs may be stored as a group, such that whenIMD 102 generates and delivers electrical stimulation therapy via aselected group, IMD 102 delivers electrical stimulation signal via twoor more therapy programs. IMD 102 may be configured to deliverelectrical stimulation defined by two or more therapy programssimultaneously or on a time-interleaved basis.

In some examples, IMD 102 is configured to deliver a recharge signal(e.g., one or more recharge pulses or other waveforms), which may helpbalance a charge accumulation that may occur within tissue proximate theelectrodes used to deliver the electrical stimulation. The rechargesignal may also be referred to as a “recovery signal” or a “chargebalancing signal” and may have a polarity opposite to that of theelectrical stimulation signal generated and delivered by IMD 102. Whilerecharge pulses are primarily referred to herein, in other examples, arecharge signal can have any suitable waveform.

A user, such as a clinician or patient 12, may interact with a userinterface of an external programmer 104 to program IMD 102. Programmingof IMD 102 may refer generally to the generation and transfer ofcommands, programs, or other information to control the operation of IMD102. In this manner, IMD 102 may receive the transferred commands andprograms from programmer 104 to control stimulation therapy. Forexample, external programmer 104 may transmit therapy programs,stimulation parameter adjustments, therapy program selections, therapyprogram group selections, user input, or other information to controlthe operation of IMD 102, e.g., by wireless telemetry or wiredconnection.

In some cases, external programmer 104 may be characterized as aphysician or clinician programmer if it is primarily intended for use bya physician or clinician. In other cases, external programmer 104 may becharacterized as a patient programmer if it is primarily intended foruse by a patient. A patient programmer may be generally accessible topatient 12 and, in many cases, may be a portable device that mayaccompany patient 12 throughout the patient's daily routine. Forexample, a patient programmer may receive input from patient 12 when thepatient wishes to terminate or change stimulation therapy. In general, aphysician or clinician programmer may support selection and generationof programs by a clinician for use by IMD 102, whereas a patientprogrammer may support adjustment and selection of such programs by apatient during ordinary use. In other examples, external programmer 104may be included, or part of, an external charging device that rechargesa power source of IMD 102. In this manner, a user may program and chargeIMD 102. using one device, or multiple devices.

As described herein, information may be transmitted between externalprogrammer 104 and IMD 102. Therefore, IMD 102 and programmer 104 maycommunicate via wireless communication using any techniques known in theart. Examples of communication techniques may include, for example,radiofrequency (RF) telemetry and inductive coupling, but othertechniques are also contemplated. In some examples, programmer 104 mayinclude a communication head that may be placed proximate to thepatient's body near the IMD 102 implant site in order to improve thequality or security of communication between IMD 102 and programmer 104.Communication between programmer 104 and IMD 102 may occur during powertransmission or separate from power transmission.

In some examples, IMD 102 delivers a recharge signal after delivery ofmultiple pulses of an electrical stimulation signal, which may bedefined by one therapy program or by multiple therapy programs. Thus,rather than charge balancing on a pulse-by-pulse basis (e.g., deliveringone recharge pulse after each electrical stimulation pulse), in someexamples, IMD 102 delivers one or more recharge pulses after delivery oftwo or more electrical stimulation pulses. In some examples, IMD 102delivers an electrical stimulation signal to patient 12. according tomultiple therapy programs by at least interleaving pulses of two or moretherapy programs, the pulses having a first polarity. In some of theseexamples, IMD 102 may wait to deliver one or more recharge pulses untilafter one or more pulses of each of the therapy programs are delivered,each recharge pulse having a second polarity opposite to the firstpolarity. Thus, in some examples, IMD 102 may not deliver any rechargesignals between therapy programs, but, rather, may withhold the deliveryof one or more recharge signals until after IMD 102 delivers a pluralityof pulses according to two or more therapy programs.

As described below, IMD 102, in response to commands from externalprogrammer 104, may be configured to deliver electrical stimulationtherapy according to a plurality of electrical stimulation therapyparameter sets to a plurality of respective target tissue areas of thespinal column 20 of patient 12 via electrodes (not depicted) on leads16. IMD 102 may be configured to deliver the electrical stimulationtherapy according to the plurality of electrical stimulation therapyparameter sets simultaneously (e.g., where a pulse from one stimulationtherapy is delivered simultaneous with a pulse from another stimulationtherapy) or time-interleaved (e.g., pulses from each stimulation therapyare alternated in time). In some examples, each electrical stimulationtherapy program comprises electrical stimulation pulses at a highfrequency, e.g., a frequency of greater than 1,000 Hertz, a frequency ofgreater than approximately 1.2 kHz, a frequency of greater than 1.5 kHz,or a frequency between 5 and 10 kHz.

High-frequency stimulation may be effective in alleviating or reducingchronic pain while avoiding the need to cause paresthesia in patients.However, as the frequency of the electrical stimulation increases beyonda certain frequency threshold, such as 1,000 Hertz for example, apatient may not notice any difference with higher frequencies or deriveany further therapeutic benefit, such as reduction in the severity ofone or more symptoms of a disease of the patient. Therefore, IMD 102 maydeliver electrical stimulation from different electrode combinations(e.g., effecting different tissue sites using multiple programs) withouttissues within the zones of stimulation of the multiple programs andsubject to pulses from electrical stimulation therapy according todifferent electrical stimulation therapy parameter sets perceiving anydifferences in stimulation. In sonic examples, the zones of stimulationfrom electrical stimulation therapy according to a plurality ofelectrical stimulation therapy parameter sets delivered by each set ofelectrodes do not overlap with one another. In other examples, whenelectrical stimulation therapy according to the electrical stimulationtherapy parameter sets are delivered on a time-interleaved basis withone another and the respective zones of stimulation reach a commontissue area, the tissue affected by both zones of stimulation from theplurality of electrical stimulation pulses delivered by each set ofelectrodes perceives an effective pulse rate, or frequency of a combinedelectrical stimulation at that common target tissue site. In someexamples, the combined or effective pulse rate has a uniformdistribution of pulses such that the combined pulse burst has a uniformfrequency. In other examples, the combined or effective pulse rate has anon-uniform distribution of pulses (e.g., the pulses have differinginter-pulse intervals and/or different pulse widths within a certainperiod of time). Thus, delivering electrical stimulation therapyaccording to a plurality of electrical stimulation therapy parametersets on a time-interleaved basis with one another may cause, at theintersection of each electric field of each respective electricaltherapy stimulation therapy, specific areas of high frequency therapythat are not necessarily located immediately next to the electrodes.This time-interleaved higher frequency stimulation delivery facilitatesmore flexibility in targeting the higher frequency to the targetedlocation that may not be immediately near an electrode and can reduceside effects if providing high frequency stimulation is not desired inclose proximity to the electrodes. Further description of the use ofinterleaving a plurality of lower-frequency electrical stimulationtherapy programs to deliver an effective higher-frequency electricalstimulation program to a target tissue area are described in U.S. patentapplication Ser. No. 15/623,141 to Torgerson, entitled “DELIVERY OFINDEPENDENT INTERLEAVED PROGRAMS TO PRODUCE HIGHER-FREQUENCY ELECTRICALSTIMULATION THERAPY” and filed on Jul. 14, 2017, the entire content ofwhich is incorporated by reference herein.

In some examples, IMD 102 is configured to generate and deliverelectrical stimulation therapy according to a plurality of electricalstimulation therapy parameter sets to patient 12 via a plurality ofelectrodes, e.g., of leads 16 and/or a housing of IMD 102, eachelectrical stimulation therapy parameter set of the plurality ofelectrical stimulation therapy parameter sets delivered via two or moreelectrodes of the plurality of electrodes. Each electrical stimulationtherapy signal may have a frequency of greater than approximately 1000Hertz in some examples, greater than approximately 1,200 Hertz in someexamples, greater than 1,500 Hertz in other examples, greater than 5,000Hertz in other examples, or greater than 10,000 Hertz in still otherexamples. Additionally, each electrical stimulation therapy signal mayhave a frequency of less than approximately 20,000 Hertz in someexamples, less than 10,000 Hertz in other examples, or less than 5,000Hertz in still other examples.

In some examples, each electrical stimulation therapy signal may have afrequency greater than approximately 900 Hertz and less thanapproximately 1,500 Hertz. In other examples, each electricalstimulation therapy signal may have a frequency may be greater thanapproximately 1,200 Hertz and less than approximately 20,000 Hertz, orgreater than approximately 1,200 Hertz and less than approximately 5.000Hertz in other examples. In some examples, each electrical stimulationtherapy has a frequency of approximately 4,800 Hertz. In a differentexample, the frequency may be greater than approximately 5,000 Hertz andless than approximately 20,000 Hertz, greater than approximately 5,000Hertz and less than approximately 10,000 Hertz in other examples, andgreater than approximately 10,000 Hertz and less than approximately20,000 Hertz in still other examples. In some examples, the signal has afrequency of approximately 10,000 Hertz.

In some examples, the amplitude and pulse width of the electricalstimulation signal are selected such that a stimulation intensity levelof the electrical stimulation signal is less than a perception orparesthesia threshold intensity level for patient 12. Stimulationdelivered at an intensity that is less than a perception or paresthesiathreshold intensity level for patient 12 may be referred to assub-threshold stimulation. The perception threshold is the lowest levelof electrical stimulation that is sufficient for the patient to perceivethat the IMD is delivering electrical stimulation. The paresthesiathreshold is the lowest level of electrical stimulation that causesparesthesia in the patient. Paresthesia may cause discomfort in thepatient, and is sometimes described as a “pins and needles” sensation,but that discomfort or tingling may mask and be more tolerable than painotherwise felt by the patient. A clinician may select one or moreparameters of the electrical stimulation therapy, and titrate the one ormore parameters until the electrical stimulation therapy is less than aperception or paresthesia threshold intensity level for patient 12. Inone example, the electrical stimulation signal has a current amplitudein a range of 0.1 microamps to 100 milliamps. In another example, theamplitude may be selected to be in a range of about 0.1 milliamps toabout 25 milliamps, such as in a range of about 0.5 milliamps to about 5milliamps. In another example, the electrical stimulation signal has avoltage amplitude in a range of 10 millivolts to 14 Volts. In anotherexample, the electrical stimulation signal has a voltage amplitude in arange of 50 millivolts to 14 Volts, such as in a range of about 500millivolts to about 5 Volts.

In one example, the electrical stimulation signal comprises of one ormore electrical pulses (e.g., a pulse train), wherein each pulse has apulse width in a range of 2 microseconds to 833 microseconds. In afurther example, each pulse has a pulse width of about 20 microsecondsto about 60 microseconds. In one example, the electrical stimulationsignal comprises of one or more electrical pulses (e.g., a pulse train),wherein each pulse has a pulse width in a range of 30 microseconds to 60microseconds. In one example, the electrical stimulation signalcomprises of one or more electrical pulses (e.g., a pulse train),wherein each pulse has a pulse width of approximately 50 microseconds.In one example, the electrical stimulation signal comprises of one ormore electrical pulses (e.g., a pulse train), wherein each pulse has apulse width of approximately 60 microseconds.

In some examples, IMD 102 delivers the pulses of the electricalstimulation signal via a plurality of different electrode combinations.For example, IMD 102 may alternate delivery of pulses between twodifferent electrode combinations (e.g., different electrical stimulationtherapy parameter sets), or may otherwise interleave the pulses usingtwo or more electrode combinations in any suitable order. In someexamples, IMD 102 may deliver time-interleaved pulses via two, three,four or more electrode combinations. IMD 102 may alternate betweendelivery of a single pulse on each of two or more electrode combinationsover a series of time intervals. In some examples, zones of stimulationgenerated by each electrode combination do not overlap such that eachtarget tissue site receives electrical stimulation from only a singlerespective electrode combination. In other examples, zones ofstimulation generated by each electrode combination overlap with zonesof stimulation generated by each other electrode combination so as tocreate a combined zones of stimulation at a target tissue site. In otherexamples, the zones of stimulation generated by each electrodecombination overlap with zones of stimulation generated by each otherelectrode combination. As an illustration, IMD 102 may deliver a firstpulse in a first time interval via a first electrode combination, asecond pulse in a second time interval via a second electrodecombination, a third pulse in a third time interval via a thirdelectrode combination, and a fourth pulse in a fourth time interval viaa fourth electrode combination, and repeat this process, e.g., on aperiodic basis. In other examples, IMD 102 may alternate betweendelivery of multiple pulses between two or more different electrodecombinations over successive time intervals. As an illustration, IMD 102may deliver a two or more first pulses in a first time interval via afirst electrode combination, two or more second pulses in a second timeinterval via a second electrode combination, two or more third pulses ina third time interval via a third electrode combination, and two or morefourth pulses in a fourth time interval via, a fourth electrodecombination, and repeat this process, e.g., on a periodic basis. In oneexample, each electrode combination comprises one electrode functioningas an anode and another electrode functioning as a cathode, and theseelectrodes are unique to the electrode combination, i.e., the electrodesused for delivery of stimulation pulses in one electrode combinationsare not used in any of the other electrode combinations. In anotherexample, each electrode combination comprises a plurality of electrodesfunctioning as anodes in conjunction with a cathode and/or a pluralityof electrodes functioning as cathodes in conjunction with an anode, andeach of these pluralities of electrodes is unique to the electrodecombination.

In some examples where IMD 102 delivers electrical stimulation therapyaccording to the different electrical stimulation therapy parameter setson a time-interleaved basis with one another, IMD 102 may cease deliveryof a first electrical stimulation therapy for a period of time prior toswitching to the next electrical stimulation therapy. In other words,IMD 102 may deliver a first electrical stimulation therapy and ceasedelivery of all electrical stimulation therapy for a period of time.After the period of time has elapsed, IMD 102 may deliver a secondelectrical stimulation therapy and then cease delivery of all electricalstimulation therapy for the period of time. After the period of time haselapsed again, IMD 102 may deliver a third electrical stimulationtherapy, etc. By ceasing delivery of electrical stimulation therapybetween different electrical stimulation therapy parameter sets, IMD 102may avoid overstimulating the target tissue sites of patient 12.Furthermore, by ceasing delivery of electrical stimulation therapybetween different electrical stimulation therapy parameter sets, IMD 102may ensure that any effects on patient 12 of a second electricalstimulation therapy are due to the second electrical stimulationtherapy, and not due to residual energy from a first electricalstimulation therapy. In some examples, IMD 102 may cease delivery of allstimulation during the transition between the different electricalstimulation therapy parameter sets for a period of time of about 500milliseconds. In other examples, the period of time is less than about500 milliseconds.

In a typical lead implantation procedure, the clinician may insert oneor more electrode leads 16 along spinal cord 20 of patient 12. Theclinician may attempt to place leads 16 such that at least one electrodeof lead 16A and at least one electrode of lead 16B are on opposite sidesof spinal cord 20. However, it is presently not well understood where,along spinal cord 20, an optimal location for delivery of electricalstimulation may lie such that the electrical stimulation exhibitsefficacy in treating a condition of patient 12. For example, such alocation may differ from patient to patient and may also depend on theproximity of individual electrodes along leads 16 to one another and onthe individual electrical characteristics of each of the electrodes.

After implantation of the leads, the clinician may test the placement ofelectrodes. In some examples, the clinician connects the leads to anexternal medical device. The clinician may test various electricalstimulation therapy parameter sets to determine an electricalstimulation therapy that effectively treats a condition of patient 12.For example, the clinician may test various combinations of electrodesand different electrical stimulation therapy parameters, etc. todetermine an electrical stimulation therapy that effectively suppressesone or more symptoms of the disease of patient 12, such as chronic pain.Such a trial outpatient evaluation may occur over about 10 days.However, in some examples, patient 12 may require several days todemonstrate a response to the electrical stimulation, such asparesthesia, pain relief, or the suppression of the one or more symptomsof the disease. Thus, if the clinician were to test only a singleelectrical stimulation therapy parameter set at a time, he or she wouldbe unable to test more than two or three different electricalstimulation therapy parameter sets before the time for the outpatientevaluation ends.

In accordance with the techniques of the disclosure, medical system 100is configured to deliver, via a plurality of electrode combinations ofelectrodes disposed along lead 16 of a medical device, such as IMD 102,a plurality of electrical stimulation therapy programs to patient 12. Insome examples, the medical device delivers each of the plurality ofelectrical stimulation therapy programs on a time-interleaved basis withone another, while in other examples, the medical device delivers eachof the plurality of electrical stimulation therapy programssubstantially simultaneously. Furthermore, such electrical stimulationis delivered via a plurality of electrodes to a plurality of targettissue areas over a large portion of spinal cord 20 of patient 12. Byensuring maximal coverage of spinal cord 20, the clinician may quicklydetermine (e.g., within one test period of about 3 days) whether theelectrical stimulation therapy is capable of treating a condition ofpatient 12. In this fashion, the techniques of the disclosure may allowfor the rapid determination of whether electrical stimulation therapy iseffective for treating a condition of patient 12.

After determining whether the electrical stimulation is effective fortreating a condition of patient 12, the clinician may implant animplantable medical device, such as IMD 102, within patient 12 andconnects the leads to the implantable medical device. However, in someexamples, the above determination of whether the electrical stimulationis effective for treating the condition of patient 12 is performed afterimplanting IMD 102. At this time, the clinician may attempt to removeone or more electrodes that deliver the electrical stimulation therapyso as to reduce power consumption of IMD 102. In some examples, thisoccurs in an outpatient setting. As one example, IMD 102 iterativelydelivers electrical stimulation via subsets of the plurality ofelectrodes to subsets of the plurality of target tissue areas. In thisfashion, the techniques of the disclosure may determine a primary set ofelectrodes 116, 118 that delivers electrical stimulation therapy to atissue area smaller than the collective plurality of target tissue areaswhile maintaining effective therapy. In turn, IMD 102 may conserveenergy by delivering electrical stimulation via the primary set ofelectrodes to this smaller tissue area. Such techniques may reduce thepower usage required to deliver the electrical stimulation over timewhile maintaining the desired therapy initially provided by delivery ofthe electrical stimulation therapy to the plurality of target tissueareas.

In one example of the techniques of the disclosure, after the clinicianimplants the leads, the clinician selects a first electrode combinationof a medical device, such as an external medical device or animplantable medical device such as IMD 102, that is configured todeliver electrical stimulation via the first electrode combination to afirst plurality of target tissue sites along spinal cord 20 of patient12. The medical device controls delivery of the electrical stimulationto the first plurality of target tissue sites along spinal cord 20 ofpatient 12. In one example, the clinician selects a first set ofelectrodes configured to deliver a first electrical pulse train having afrequency of approximately 1,000 Hertz to a set of four tissue sitesalong the T9-T10 disc space of patient 12 (e.g., tissue sites 14A, 14B,14C, and 14D). If patient 12 does not experience pain relief afterseveral days, the clinician selects a second electrode combinationconfigured to deliver electrical stimulation to a second plurality oftarget tissue sites along the spinal cord of patient 12 (e.g., tissuesites 15A, 15B, 15C, and 15D). In this example, the clinician may selecta second set of electrodes configured to deliver a second electricalpulse train having a frequency of approximately 1,000 Hertz to the setof four tissue sites 15A, 15B, 15C, and 15D along the T9-T10 disc spaceof patient 12. In this example, upon determining that the secondelectrical pulse train delivered to the set of four tissue sites 15A,15B, 15C, and 15D treats a condition of patient 12, the clinician mayselect the second set of electrodes for subsequent delivery ofelectrical stimulation therapy to patient 12.

In some examples, after the clinician has determined that electricalstimulation delivered to a plurality of tissue sites results intreatment of the patient's condition, the clinician disconnects anexternal medical device from the leads implanted within patient 12,implants an implantable medical device, such as IMD 102, within patient12, and connects the leads to IMD 102. Further, the clinician mayattempt to reduce the number of electrodes, or number of programs, forsubsequent therapy while maintaining effective treatment. This reductionin electrodes and stimulation coverage area may be possible forhigh-frequency electrical stimulation since the therapeutic effect maybe generated only from high-frequency electrical stimulation deliveredto a specific tissue site while high frequency electrical stimulationdelivered to extraneous tissue sites may not affect the therapeuticeffect. Furthermore, the system may iteratively test the efficacy ofeach individual electrode combination of the electrodes used to deliverthe plurality of electrical stimulation therapy programs by removing oneor more of the 1,000 Hertz programs. As one example, the clinician mayselect a third set of electrodes configured to deliver a thirdelectrical pulse train having a frequency of approximately 1,000 Hertzto a set of two tissue sites 15A and 15B along the T9-T10 disc space ofpatient 12. If patient 12 does not experience pain relief after severaldays, the clinician selects a fourth electrode combination configured todeliver a fourth electrical pulse train having a frequency ofapproximately 1,000 Hertz to a set of two tissue sites 15C and 15D alongthe T9-T10 disc space of patient 12. In this example, upon determiningthat the fourth electrical pulse train delivered to the set of twotissue sites 15C and 15D treats a condition of patient 12, the clinicianmay select the second set of electrodes for subsequent delivery oftherapy to patient 12.

In another example, instead of removing electrodes to try and reduce thearea (or tissue sites) of the effective stimulation therapy, the systemmay isolate electrode combinations or individual programs to evaluatesmall tissue areas and work larger until the therapy can be maintained.For example, the clinician may select a fifth set of electrodesconfigured to deliver a fifth electrical pulse train having a frequencyof approximately 1,000 Hertz to only tissue site 15C along the T9-T10disc space of patient 12. If patient 12 does not experience pain reliefafter several days, the clinician selects a sixth electrode combinationconfigured to deliver a sixth electrical pulse train having a frequencyof approximately 1,000 Hertz to only tissue site 15D along the T9-T10disc space of patient 12, In this example, upon determining that thesixth electrical pulse train delivered to tissue site 15D treats acondition of patient 12, the clinician may select the sixth set ofelectrodes for subsequent delivery of therapy to patient 12.

As yet another example where the clinician iteratively tests theefficacy of each individual electrode combination by removing some ofthe 1,000 Hertz programs, the clinician selects a first combination ofelectrodes configured to deliver a first electrical pulse train having afrequency of approximately 1,000 Hertz to a set of four tissue sitesalong the T9-T10 disc space of patient 12 (e.g., tissue sites 14A, 14B,14C, and 14D). If, after several days, patient 12 does not experiencepain relief, the clinician may select a second combination of electrodesconfigured to deliver a first electrical pulse train having a frequencyof approximately 1,000 Hertz to a set of four tissue sites along theT9-T10 disc space of patient 12 (e.g., tissue sites 15A, 15B, 15C, and15D). Alternatively, if, after several days, patient 12 experiences painrelief, the clinician removes one subset of electrodes (e.g., thoseconfigured to provide therapy to tissue site 14A) and continuesdelivering electrical stimulation to tissue sites 14B, 14C, and 14D. If,after another several days, patient 12 continues experiencing painrelief, the clinician removes another subset of electrodes (e.g., thoseconfigured to provide therapy to tissue site 14B) and continuesdelivering electrical stimulation to tissue sites 14C and 14D. Ifpatient 12 experiences a return of pain, the clinician may restore theremoved subset of electrodes (e.g., those configured to provide therapyto tissue site 14B), remove a different subset of electrodes (e.g.,those configured to provide therapy to tissue site 14C) and continueiteratively testing delivery of electrical stimulation to tissue sites14B and 14D. The clinician may continue such iterative testing ofelectrode combinations until the clinician determines a minimum numberof electrode combinations that effectively treat the condition ofpatient 12.

In other examples, after a plurality of electrical stimulation therapyparameter sets are determined to be effective in treating the patient,the system may remove of one or more electrodes (e.g., one or moreelectrical stimulation therapy parameter sets) according to apredetermined scheme e.g., by removing electrode combinations inproximal or distal order along a lead) or by random selection. In oneexample, the clinician may continue to remove electrode combinationsuntil every combination of electrodes has been tested individually forefficacy. In another example, the clinician may continue to removeelectrode combinations until the clinician determines a minimum numberof electrode combinations required to provide electrical stimulationtherapy treats a condition of patient 12, such as suppressing pain.

In some examples, the iterative testing of combinations of electrodesmay be performed by the clinician in an outpatient setting aftercompletion of an implantation procedure of IMD 102. In other examples,IMD 102 may iteratively test combinations of electrodes on a periodicbasis, e.g., monthly, bimonthly, or yearly. In the examples describedabove, the terms evaluation period, test period, and trial period areused interchangeably and refer to the time period that the IMDiteratively tests combinations of electrodes. Such a test period maylast for about one to two weeks or less. Further, upon determining aprimary set of electrodes that effectively treats a condition of patient12, as described above, IMD 102 delivers electrical stimulation topatient 12 over a chronic period. As used throughout, the chronic periodrefers to the time period that IMD 102 delivers electrical stimulationtherapy to patient 112 to treat the condition of patient 112. Thechronic time period may be the operable lifetime of IMD 102. Typically,the test period is much shorter than the chronic period and used forevaluation of therapy.

Thus, by removing electrodes or programs that do not contribute to thetreatment, the techniques of the disclosure may reduce the number ofelectrodes delivering electrical stimulation, and thereby reduce thepower consumed by IMD 102 when delivering therapy. In other words,removing electrodes or programs may reduce the area of stimulation andcurrent used by the IMD 102. By reducing the power consumption of IMD102, the techniques of the disclosure may increase the time that IMP 102may function without recharging, in the case of a rechargeable IMD, orincrease the operative life of a non-rechargeable IMD. In addition, thetechniques of the disclose may increase the number of tissue sites (orarea of tissue) that a clinician may test in a limited amount of time,thereby increasing the chance of identifying electrical stimulationeffective in alleviating symptoms of pain of patient 12. Then, afterstimulation is deemed to be effective, the system can work onidentifying electrode combinations with fewer electrodes to reduce thepower consumption of IMD 102 while maintaining therapy efficacy.

Although IMD 102 is generally described herein, techniques of thisdisclosure may also be applicable to external or partially externalmedical device in other examples. For example, IMD 102 may instead beconfigured as an external medical device coupled to one or morepercutaneous medical leads. The external medical device may be achronic, temporary, or trial electrical stimulator. In addition, anexternal electrical stimulator may be used in addition to one or moreIMDs 102 to deliver electrical stimulation described herein.

FIG. 2 is a block diagram of the example IMD 102 of FIG. 1. In theexample shown in FIG. 2, IMD 102 includes processing circuitry 210,memory 211, stimulation generator 202, sensing circuitry 204, telemetrycircuitry 208, sensor 212, and power source 220. Memory 211 may includeany volatile or non-volatile media, such as a random access memory(RAM), read only memory (ROM), non-volatile RAM (NVRAM), electricallyerasable programmable ROM (EEPROM), flash memory, and the like. Memory211 may store computer-readable instructions that, when executed byprocessing circuitry 210, cause IMD 102. to perform various functions.Memory 211 may be a storage device or other non-transitory medium.

In the example shown in FIG. 2, memory 211 stores therapy programs 214and sense electrode combinations and associated stimulation electrodecombinations 218 in separate memories within memory 211 or separateareas within memory 211. Each stored therapy program 214 defines aparticular set of electrical stimulation parameters (e.g., a therapyparameter set), such as a stimulation electrode combination, electrodepolarity, current or voltage amplitude, pulse width, and pulse rate. Insome examples, individual therapy programs may be stored as a therapygroup, which defines a set of therapy programs with which stimulationmay be generated. The stimulation signals defined by the therapyprograms of the therapy group include stimulation pulses that may bedelivered together on an overlapping (e.g., simultaneous) ornon-overlapping (e.g., time-interleaved) basis.

The techniques of the disclosure are described in some examples asinterleaving stimulation pulses on a non-overlapping (time-interleaved)basis. However, in some examples, the techniques of the disclosure mayallow for interleaving stimulation pulses delivered via different setsof electrodes on an at least partially overlapping, or fullyoverlapping, basis. Overlapping of the recharge or recovery pulses ofthe different programs or electrode combinations may be useful becauseit may allow more time to discharge series capacitors on the electrodes.This may allow the system to operate more efficiently. For example, eachof the plurality of electrical stimulation programs delivers therapypulses on unique electrodes. However, during the time of the recoverypulse, each of the electrodes used in all of the electrical stimulationtherapy programs are tied together on the IMD and connected to the body.This allows the series capacitors of the electrodes to simultaneouslydischarge to balance the therapy pulses. Such a system allows forrecovery pulses having a lower amplitude than other systems, andtherefore, such a system may disperse the energy more uniformly to thetissue of the patient instead of localizing it to the specific electrodecombination.

Accordingly, in some examples, stimulation generator 202 generateselectrical stimulation signals in accordance with the electricalstimulation parameters noted above. Other ranges of therapy parametervalues may also be useful, and may depend on the target stimulation sitewithin patient 112. While stimulation pulses are described, stimulationsignals may be of any form, such as continuous-time signals (e.g., sinewaves) the like.

Processing circuitry 210 may include any one or more of amicroprocessor, a controller, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA), discrete logic circuitry, or any other processingcircuitry configured to provide the functions attributed to processingcircuitry 210 herein may be embodied as firmware, hardware, software orany combination thereof. Processing circuitry 210 controls stimulationgenerator 202 according to therapy programs 214 stored in memory 211 toapply particular stimulation parameter values specified by one or moreof programs, such as amplitude, pulse width, and pulse rate.

In the example shown in FIG. 2, the set of electrodes 116 includeselectrodes 116A, 116B, 116C, and 116D, and the set of electrodes 118includes electrodes 118A, 118B, 118C, and 118D. Processing circuitry 210also controls stimulation generator 202 to generate and apply thestimulation signals to selected combinations of electrodes 116, 118. Insome examples, stimulation generator 202 includes switch circuitry thatselectively transmits stimulation signals to selected conductors withinleads 16, which, in turn, deliver the stimulation signals acrossselected electrodes 116, 118. Such switch circuitry ma y be a switcharray, switch matrix, multiplexer, or any other type of switchingcircuitry configured to selectively couple stimulation energy toselected electrodes 116, 118 and to selectively sense bioelectricalneural signals of spinal cord 20 with selected electrodes 116, 118,

In other examples, however, stimulation generator 202 does not includeswitch circuitry, In these examples, stimulation generator 202 comprisesa plurality of pairs of voltage sources, current sources, voltage sinks,or current sinks connected to each of electrodes 116, 118 such that eachpair of electrodes has a unique signal generator. In other words, inthese examples, each of electrodes 116, 118 is independently controlledvia its own signal generator (e.g., via a combination of a regulatedvoltage source and sink or regulated current source and sink), asopposed to switching signals between electrodes 116, 118.

Stimulation generator 202 may be a single channel or multi-channelstimulation generator. In particular, stimulation generator 202 may becapable of delivering a single stimulation pulse or multiple stimulationpulses at a given time via a single electrode combination or multiplestimulation pulses at a given time via multiple electrode combinations.In some examples, however, stimulation generator 202 may be configuredto deliver multiple channels on a time-interleaved basis. For example,switch circuitry of stimulation generator 202 may serve to time dividethe output of stimulation generator 202 across different electrodecombinations at different times to deliver multiple programs or channelsof stimulation energy to patient 112. In another example, thestimulation generator 202 may control the independent sources or sinkson a time-interleaved bases.

Electrodes 116, 118 on respective leads 16 may be constructed of avariety of different designs. For example, one or both of leads 16 mayinclude two or more electrodes at each longitudinal location along thelength of the lead, such as multiple electrodes at different perimeterlocations around the perimeter of the lead at each of the locations A,B, C, and D. On one example, the electrodes may be electrically coupledto switch circuitry 206 via respective wires that are straight or coiledwithin the housing the lead and run to a connector at the proximal endof the lead. In another example, each of the electrodes of the lead maybe electrodes deposited on a thin film. The thin film may include anelectrically conductive trace for each electrode that runs the length ofthe thin film to a proximal end connector. The thin film may then bewrapped (e.g., a helical wrap) around an internal member to form thelead 16. These and other constructions may be used to create a lead witha complex electrode geometry.

Although sensing circuitry 204 is incorporated into a common housingwith stimulation generator 202 and processing circuitry 210 in FIG. 2,in other examples, sensing circuitry 204 may be in a separate housingfrom IMD 102 and may communicate with processing circuitry 210 via wiredor wireless communication techniques. Example bioelectrical signalsinclude, but are not limited to, a signal generated from local fieldpotentials within one or more regions of spinal cord 20.

Sensor 212 may include one or more sensing elements that sense values ofa respective patient parameter. For example, sensor 212 may include oneor more accelerometers, optical sensors, chemical sensors, temperaturesensors, pressure sensors, or any other types of sensors. Sensor 212 mayoutput patient parameter values that may be used as feedback to controldelivery of therapy. IMD 102 may include additional sensors within thehousing of IMD 102 and/or coupled via one of leads 16 or other leads. Inaddition, IMD 102 may receive sensor signals wirelessly from remotesensors via telemetry circuitry 208, for example. In some examples, oneor more of these remote sensors may be external to patient (e.g.,carried on the external surface of the skin, attached to clothing, orotherwise positioned external to the patient)

Telemetry circuitry 208 supports wireless communication between IMD 102and an external programmer 104 or another computing device under thecontrol of processing circuitry 210. Processing circuitry 210 of IMD 102may receive, as updates to programs, values for various stimulationparameters such as amplitude and electrode combination, from programmer104 via telemetry circuitry 208. The updates to the therapy programs maybe stored within therapy programs 214 portion of memory 211. Telemetrycircuitry 208 in IMD 102, as well as telemetry circuitry in otherdevices and systems described herein, such as programmer 104, mayaccomplish communication by radiofrequency (RF) communicationtechniques. In addition, telemetry circuitry 208 may communicate withexternal medical device programmer 104 via proximal inductiveinteraction of IMD 102 with programmer 104. Accordingly, telemetrycircuitry 208 may send information to external programmer 104 on acontinuous basis, at periodic intervals, or upon request from IMD 102 orprogrammer 104.

Power source 220 delivers operating power to various components of IMD102. Power source 220 may include a small rechargeable ornon-rechargeable battery and a power generation circuit to produce theoperating power. Recharging may be accomplished through proximalinductive interaction between an external charger and an inductivecharging coil within IMD 220. In some examples, power requirements maybe small enough to allow IMD 220 to utilize patient motion and implementa kinetic energy-scavenging device to trickle charge a rechargeablebattery. In other examples, traditional batteries may be used for alimited period of time.

According to the techniques of the disclosure, telemetry circuitry 208of IMD 102 receives commands from an external programmer 104. Inresponse to these commands, processing circuitry 210 of IMD 102 deliversa plurality of electrical stimulation therapy programs to a plurality oftarget tissue areas of the spinal column 20 of patient 12 via electrodes116, 118 of leads 16.

In some examples, IMD 102 is configured to generate and deliverelectrical stimulation therapy to patient 12 via two or more pairs ofelectrodes, e.g., combinations of two or more of electrodes 116A-116Dand 118A-118D, e.g., of leads 16 and/or a housing of IMD 102. In someexamples, each individual pulse train delivered on the two or more pairsof electrodes has a frequency in a range of about 1000 Hertz to about1500 Hertz, although frequencies lower and higher than this range mayalso be used. The amplitude and pulse width of the electricalstimulation signal are selected such that a stimulation intensity levelof the electrical stimulation signal is less than a perception orparesthesia threshold intensity level for patient 12. For example, in acurrent-controlled implementation, the amplitude may be selected to bein a range of 0.1 microamps to 100 milliamps. In another example, theamplitude may be selected to be in a range of about 0.1 milliamps toabout 25 milliamps, such as in a range of about 0.5 milliamps to about 5milliamps. In another example, in a voltage-controlled implementation,the amplitude may be selected to be in a range of 10 millivolts to 14Volts. In another example, the voltage amplitude may be selected to bein a range of about 50 millivolts to about 14 volts, such as in a rangeof about 500 millivolts to about 5 Volts.

In one example, the electrical stimulation signal comprises of one ormore electrical pulses (e.g., a pulse train), wherein each pulse has apulse width in a range of 2 microseconds to 833 microseconds. In afurther example, each pulse has a pulse width of about 20 microsecondsto about 60 microseconds, In one example, the electrical stimulationsignal comprises of one or more electrical pulses (e.g., a pulse train),wherein each pulse has a pulse width in a range of 30 microseconds to 60microseconds. In one example, the electrical stimulation signalcomprises of one or more electrical pulses (e.g., a pulse train),wherein each pulse has a pulse width of approximately 50 microseconds.In one example, the electrical stimulation signal comprises of one ormore electrical pulses e.g., a pulse train), wherein each pulse has apulse width of approximately 60 microseconds.

In some examples, IMD 102 delivers the pulses of the electricalstimulation signal via different electrode combinations of two or moreof electrodes 116A-116D and 118A-118D and a housing of IMD 102. Forexample, IMD 102 may alternate delivery of pulses between two or moredifferent electrode combinations, or may otherwise interleave the pulsesusing two or more electrode combinations in any suitable order. In oneexample, each electrode combination comprises at least one electrodefunctioning as an anode and at least one other electrode functioning asa cathode, and these electrodes are unique to the electrode combinationin that the same electrodes are not used in other electrode combinationsthat are used to delivery time-interleaved stimulation pulses.

The electrical stimulation therapy signal may have a frequency ofgreater than approximately 1000 Hertz in some examples, greater thanapproximately 1,200 Hertz in some examples, greater than 1,500 Hertz inother examples, greater than 5,000 Hertz in other examples, or greaterthan 10,000 Hertz in still other examples. Additionally, the electricalstimulation therapy signal may have a frequency of less thanapproximately 20,000 Hertz in some examples, less than 10,000 Hertz inother examples, or less than 5,000 Hertz in still other examples. Insome examples, the frequency may be greater than approximately 1,200Hertz and less than approximately 20,000 Hertz, or greater thanapproximately 1,200 Hertz and less than approximately 5,000 Hertz inother examples. In some examples, the signal has a frequency ofapproximately 4,800 Hertz. In a different example, the frequency may begreater than approximately 5,000 Hertz and less than approximately20,000 Hertz, greater than approximately 5,000 Hertz and less thanapproximately 10,000 Hertz in other examples, and greater thanapproximately 10,000 Hertz and less than approximately 20,000 Hertz instill other examples. In some examples, the signal has a frequency ofapproximately 10,000 Hertz.

In another example, in response to telemetry circuitry 208 receivingcommands from an external programmer 104, processing circuitry 210 ofIMD 102 selects the target tissue area by selecting different electrodecombinations of two or more of electrodes 116A-116D and 118A-118D and ahousing of IMD 102 that share common anodes electrodes or cathodeelectrodes. For example, processing circuitry 210 of IMD 102 selects afirst electrical stimulation therapy program delivered via a firstelectrode combination including anode electrode 116A and cathodeelectrode 118A, a second electrical stimulation therapy programdelivered via a second electrode combination including anode electrode116B and cathode electrode 118A, a third electrical stimulation therapyprogram delivered via a third electrode combination including anodeelectrode 1160 and cathode electrode 118A, and a fourth electricalstimulation therapy program delivered via a fourth electrode combinationhaving anode electrode 116D and cathode electrode 118A. In this example,the tissue proximate to the cathode electrode 118A may receive a pulsetrain signal that is a combination of the first, second, third, andfourth electrical stimulation therapy programs, while other tissues ofpatient 12 near anode electrodes 116A-116D may receive electricalstimulation due to only a single respective electrical stimulationtherapy programs.

In another example, in response to telemetry circuitry 208 receivingcommands from an external programmer 104, processing circuitry 210 ofIMD 102 selects a plurality of electrode combinations, each combinationhaving a plurality of unique anodes located down the spinal cord 20 anda plurality of common cathodes located proximate to the dorsal root ofpatient 12. In this example, for each target tissue area of theplurality of target tissue areas, processing circuitry 210 of IMD 102selects an electrode combination. For example, for a first target tissuearea, processing circuitry 201 selects a first electrical stimulationtherapy program delivered via a first electrode combination (e.g., anodeelectrode 116A and cathode electrodes 118A-118D), for a second targettissue area, processing circuitry 2010 selects a second electricalstimulation therapy program delivered via a second electrode combination(e.g., anode electrode 116B and cathode electrodes 118A-118D), for athird target tissue area, processing circuitry 2010 selects a thirdelectrical stimulation therapy program delivered via a third electrodecombination (e.g., anode electrode 116C and cathode electrodes118A-118D), and for a fourth target tissue area, processing circuitry210 selects a fourth electrical stimulation therapy program deliveredvia a fourth electrode combination (e.g., anode electrode 116D andcathode electrodes 118A-118D). In this example, a central region oftissue area of patient 12 (e.g., the tissue near cathode electrodes118A-118D) may receive electrical stimulation from each of the fourelectrode combinations 118A-118D, while other tissues of patient 12(e.g., the tissue near anode electrodes 116A-116D) may receive onlyelectrical stimulation from a single electrode combination. Bydelivering electrical stimulation according to a plurality of suchelectrical stimulation therapy parameter sets to a plurality ofrespective tissue sites 14A-14D and 15A-15D, IMD 102 may increase thelikelihood that the dorsal root area of patient 12 receives electricalstimulation from at least one of the electrical stimulation therapyparameter sets. In this fashion, the techniques of the disclosure allowfor quickly determining whether electrical stimulation therapy may treata condition of patient 12 without spending time determining whichelectrodes may be correctly positioned so as to stimulate desired targettissue regions of spinal cord 20. Although some tissues may be subjectto the zones of stimulation generated by multiple electrodecombinations, these overlapping stimulation fields at high frequencypulses may not induce any different tissue response as compared to beingsubject to only one stimulation field. For example, the response fromtissue receiving pulses at 1,000 Hz from a single electrode combinationmay be similar to the response from the same tissue receiving pulses ata collective 4,000 Hz from four different time-interleaved electrodecombinations at 1,000 Hz each. Therefore, the system may be able totrial, or evaluate, electrical stimulation efficacy from a plurality ofelectrode combinations at the same time and later reduce the electrodecombinations to identify a smaller subset of electrodes that maintainsthe similar efficacy with less power consumption.

Therefore, e.g., in a post-trial setting, after determining that theplurality of electrical stimulation therapy parameter sets results intreatment of a condition of patient 12, processing circuitry 210 of POD102 may select one or more electrical stimulation therapy parameter setsand/or electrodes to deactivate, such that the number of target tissuesites receiving electrical stimulation therapy is reduced. As an exampleof the above, and with respect to FIG. 1, processing circuitry 210 ofIMD 102 provides electrical stimulation therapy to target tissue sites14A-14D and 15A-15D. If the electrical stimulation therapy is determinedto treat a condition of patient 12, processing circuitry 210 of IMD 102deactivates electrodes providing electrical stimulation to target tissuesites 14A-14D such that only target tissue sites 15A-15D receiveelectrical stimulation.

If, subsequently, the electrical stimulation no longer treats thecondition of patient 12, then the dorsal root area of patient 12 likelylies within target tissue sites 14A-14D. In this case, processingcircuitry 210 of IMD 102 deactivates electrodes providing electricalstimulation to target tissue sites 15A-15D and reactivates electrodesproviding electrical stimulation to target tissue sites 14A-14D. If theelectrical stimulation continues to treat the condition of patient 12,then the dorsal root area of patient 12 likely lies within target tissuesites 15A-15D. Thus, by selectively activating and deactivating subsetsof electrodes such that different target tissue sites 14A-14D and15A-15D selectively receive electrical stimulation, processing circuitry210 of POD may determine a minimum number of electrodes that stimulatethe dorsal root of patient 12 so as to effectively treat the conditionof patient 12. By only using the minimum number of electrodes necessary,IMD 102 may conserve power so as to maximize the battery life of IMD 102and therefore minimize the number of recharge operations required forIMD 102.

Accordingly, the techniques of the disclosure allow an IMD 102 todeliver electrical stimulation to a large portion of a body of patient12 so as to allow a clinician to quickly determine whether theelectrical stimulation is effective in treating the condition of patient12. Furthermore, the techniques of the disclosure allow a clinician toremove ineffective electrical stimulation programs and/or electrodes soas to reduce the power consumption of the electrical stimulationprograms delivered to patient 12.

The architecture of IMD 102 illustrated in FIG. 2 is shown as anexample. The techniques as set forth in this disclosure may beimplemented in the example IMD 102 of FIG. 2, as well as other types ofsystems not described specifically herein. Nothing in this disclosureshould be construed so as to limit the techniques of this disclosure tothe example architecture illustrated by FIG. 2.

FIG. 3 is a block diagram of the example external programmer 104 ofFIG. 1. Although programmer 104 may generally be described as ahand-held device, programmer 104 may be a larger portable device or amore stationary device. In addition, in other examples, programmer 104may be included as part of an external charging device or include thefunctionality of an external charging device. As illustrated in FIG. 3,programmer 104 may include a processing circuitry 310, memory 311, userinterface 302, telemetry circuitry 308, and power source 320. Memory 311may store instructions that, when executed by processing circuitry 310,cause processing circuitry 310 and external programmer 104 to providethe functionality ascribed to external programmer 104 throughout thisdisclosure. Each of these components, or circuits, may includeelectrical circuitry that is configured to perform some or all of thefunctionality described herein. For example, processing circuitry 310may include processing circuitry configured to perform the processesdiscussed with respect to processing circuitry 310.

In general, programmer 104 comprises any suitable arrangement ofhardware, alone or in combination with software and/or firmware, toperform the techniques attributed to programmer 104, and processingcircuitry 310, user interface 302, and telemetry circuitry 308 ofprogrammer 104. In various examples, processing circuitry 310 mayinclude one or more processors, such as one or more microprocessors,DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Programmer104 also, in various examples, may include a memory 311, such as RAM,ROM, PROM, EPROM, EEPROM, flash memory, a hard disk, a CD-ROM,comprising executable instructions for causing processing circuitry 310to perform the actions attributed to it. Moreover, although processingcircuitry 310 and telemetry circuitry 308 are described as separatecircuits, in some examples, processing circuitry 310 and telemetrycircuitry 308 are functionally integrated. In some examples, processingcircuitry 310 and telemetry circuitry 308 correspond to individualhardware units, such as ASICs, DSPs, FPGAs, or other hardware units.

Memory 311 (e.g., a storage device) may store instructions that, whenexecuted by processing circuitry 310, cause processing circuitry 310 andprogrammer 104 to provide the functionality ascribed to programmer 104throughout this disclosure. For example, memory 311 may includeinstructions that cause processing circuitry 310 to obtain a parameterset from memory, select a spatial electrode movement pattern, or receivea user input and send a corresponding command to IMD 104, orinstructions for any other functionality. In addition, memory 311 mayinclude a plurality of programs, where each program includes a parameterset that defines stimulation therapy.

User interface 302 may include a button or keypad, lights, a speaker forvoice commands, a display, such as a liquid crystal (LCD),light-emitting diode (LED), or organic light-emitting diode (OLED). Insome examples the display may be a touch screen. User interface 302 maybe configured to display any information related to the delivery ofstimulation therapy, identified patient behaviors, sensed patientparameter values, patient behavior criteria, or any other suchinformation. User interface 302 may also receive user input via userinterface 302. The input may be, for example, in the form of pressing abutton on a keypad or selecting an icon from a touch screen. The inputmay request starting or stopping electrical stimulation, the input mayrequest a new spatial electrode movement pattern or a change to anexisting spatial electrode movement pattern, of the input may requestsome other change to the delivery of electrical stimulation.

Processing circuitry 310 may also control user interface 302 to displayinformation related to an anatomical atlas (e.g., an atlas of areference anatomy) and patient-specific anatomy. For example, userinterface 302 may display a representation of one or more atlas-definedanatomical structures over a representation e.g., an image) of thespecific patient anatomy. User interface 302 may present annotationtools for adjusting the structures of the atlas to the patient anatomyand receive user annotations indicating where the correspondingstructures of the patient anatomy are located and/or where the atlasshould be moved with respect to the patient anatomy. Processingcircuitry 310 may then adjust the position and/or size of the structuresof the atlas to more closely match (e.g., a best fit) to the userannotation. After the atlas has been adjusted, the user may refer to theatlas for locations of certain structures of the patient instead ofneeding to continually find desired structures based on the image of thepatient anatomy.

Telemetry circuitry 308 may support wireless communication between IMD102 and programmer 104 under the control of processing circuitry 310.Telemetry circuitry 308 may also be configured to communicate withanother computing device via wireless communication techniques, ordirect communication through a wired connection. In some examples,telemetry circuitry 308 provides wireless communication via an RF orproximal inductive medium. In some examples, telemetry circuitry 308includes an antenna, which may take on a variety of forms, such as aninternal or external antenna.

Examples of local wireless communication techniques that may be employedto facilitate communication between programmer 104 and IMD 102 includeRF communication according to the 802.11 or Bluetooth specification setsor other standard or proprietary telemetry protocols. In this manner,other external devices may be capable of communicating with programmer104 without needing to establish a secure wireless connection. Asdescribed herein, telemetry circuitry 308 may be configured to transmita spatial electrode movement pattern or other stimulation parametervalues to IMD 102 for delivery of stimulation therapy.

In some examples, selection of therapy parameters or therapy programsmay be transmitted to a medical device (e.g., IMP 102) for delivery topatient 112. In other examples, the therapy may include medication,activities, or other instructions that patient 112 must performthemselves or a caregiver perform for patient 112. In some examples,programmer 104 may provide visual, audible, and/or tactile notificationsthat indicate there are new instructions. Programmer 104 may requirereceiving user input acknowledging that the instructions have beencompleted in some examples.

According to the techniques of the disclosure, user interface 302 ofexternal programmer 104 receives a selection from a clinician of one ormore combinations of electrodes for delivery of electrical stimulationtherapy according to a plurality of electrical stimulation therapyparameter sets to patient 12. In response to the selection, processingcircuitry 310, via telemetry circuitry 308, issues instructions to IMD102 to deliver the electrical stimulation therapy according to theplurality of electrical stimulation therapy parameter sets. In responseto the instructions, IMD 102 delivers to the target tissue areaselectrical stimulation programs. In some examples, user interface 302allows for a clinician to select one or more combinations of anode andcathode electrodes for the delivery of each electrical stimulationtherapy program. In other examples, user interface 302 allows for aclinician to select a stimulation program including a desired targettissue area and desired effective frequency, and processing circuitry310 automatically determines the appropriate combination of anode andcathode electrodes in multiple electrode combinations of IMD 102 toachieve the selected stimulation program. In this example, processingcircuitry 310, via telemetry circuitry 308, issues instructions to IMD102 causing IMD 102 to select the appropriate combination of anode andcathode electrodes and deliver electrical stimulation therapy accordingto a plurality of electrical stimulation therapy parameter sets.

The architecture of programmer 104 illustrated in FIG. 3 is shown as anexample. The techniques as set forth in this disclosure may beimplemented in the example programmer 104 of FIG. 3, as well as othertypes of systems not described specifically herein. Nothing in thisdisclosure should be construed so as to limit the techniques of thisdisclosure to the example architecture illustrated by FIG. 3.

FIG. 4 is an illustration depicting an example user interface 302 for anexternal programmer 104 of FIG. 1. In the example of FIG. 4, Userinterface 302 of FIG. 6 provides representations 401A-401D(collectively, “representations 401”) of electrodes 116, 118 of IMD 102of FIG. 2 carried on axial leads. Each representation of electrodes 116,118 displays a plurality of electrodes 116 and the configuration of eachof the plurality of electrodes 116 for a respective first, second,third, and fourth electrical stimulation therapy program whosestimulation pulses may be delivered simultaneously or on atime-interleaved basis. In response to commands from a clinician,external programmer 104 may configure one or more of electrodes 116 tofunction as anodic or cathodic electrodes for a particular electricalstimulation therapy program. In the example of FIG. 4, user interface302 of external programmer 104 displays electrode 420A as an anodicelectrode and electrode 422A as a cathodic electrode for the firststimulation program. Further, user interface 302 of external programmer104 displays electrode 420B as an anodic electrode and electrode 422B asa cathodic electrode for the second stimulation program. Further, userinterface 302 of external programmer 104 displays electrode 420C as ananodic electrode and electrode 422C as a cathodic electrode for thethird stimulation program. Further, user interface 302 of externalprogrammer 104 displays electrode 420D as an anodic electrode andelectrode 422D as a cathodic electrode for the fourth stimulationprogram. As illustrated in FIG. 4, each of the anodic electrodes420A-420D and cathodic electrodes 422A-422D are different electrodes andunique to the stimulation program.

User interface 302 provides selection buttons 401A-401D for receiving acommand from a clinician to enable or disable a respective first,second, third, and fourth electrical stimulation therapy program fordelivering electrical stimulation pulses to patient 12. User interface302. further provides a selection box 404 for receiving a command from aclinician causing external programmer 104 to adjust the amplitude of therespective electrical stimulation therapy program. In the example ofFIG. 4, selection box 404 controls a voltage amplitude. However, inother examples, selection box 404 controls a current amplitude. Userinterface 302 further provides a pulse width indicator 406 fordisplaying the pulse width of electrical pulses of the respectiveelectrical stimulation therapy program and a frequency indicator 408 fordisplaying the frequency of electrical pulses of the respectiveelectrical stimulation therapy program. In some examples, user interface404 provides means to adjust the pulse width and frequency of electricalpulses of the respective electrical stimulation therapy program.

While the example of FIG. 4 provides for a sixteen-electrode system, theexample of FIG. 4 has eight electrodes of the sixteen electrodes activeand therefore provides for four simultaneous electrical stimulationprograms. However, other systems may have any number of configurableelectrodes and programs. As one example, another 16-electrode systemallows from one to eight programs to run simultaneously on unique pairsof electrodes. Further, such a system may allow 16 programs to runsimultaneously, wherein the case or housing of the IMD functions as ananode. As a further example, a 32-electrode system allows from one to 16programs to run simultaneously on unique pairs of electrodes. Further,such a system may allow 32 programs to run simultaneously, wherein thecase or housing of the IMD functions as the anode. Although each programin FIG. 4 is shown as including one cathode and one anode as a pair ofelectrodes, a single program may define an electrode combination withthree or more electrodes that have the same or a different number ofcathodes and anodes.

Accordingly, as described herein, a clinician may use an externalprogrammer 104 to instruct an IMD 102 to deliver a plurality ofelectrical stimulation therapy programs to a plurality of tissue sitesof patient 12. By delivering a plurality of such electrical stimulationtherapy programs to a plurality of tissue sites, IMD 102 may effectivelyprovide stimulation to large portions of spinal cord 20, thereforeensuring that at least some electrodes 116, 118 deliver electricalstimulation to a region of spinal cord 20 that effectively treats thecondition of patient 12.

FIGS. 5A-5B are illustrations depicting example electrode leads of theIMD 102 of FIG. 1. In the example of FIG. 5A, electrodes 116, 118 areconfigured in a substantially similar fashion to the electrodes depictedby user interface 302 of FIG. 4. For example, electrode 420A isconfigured as an anodic electrode and electrode 422A as a cathodicelectrode for the first stimulation program. Further, user interface 302of external programmer 104 displays electrode 420B as an anodicelectrode and electrode 422B is configured as a cathodic electrode forthe second stimulation program. Further, electrode 420C is configured asan anodic electrode and electrode 422C is configured as a cathodicelectrode for the third stimulation program. Further, electrode 420D isconfigured as an anodic electrode and electrode 422D is configured as acathodic electrode for the fourth stimulation program. As illustrated inFIG. 4, each of the anodic electrodes 420A-420D and cathodic electrodes422A-422D are different electrodes and unique to the stimulationprogram.

In the example configuration of FIG. 5A, external programmer 104 hasconfigured each of the first, second, third, and fourth electricalstimulation therapy programs to deliver electrical pulses at 1000 Hertz.In other words, each pair of electrodes 420 and 422 deliver electricalpulses at 1000 Hertz. Therefore, tissue at the site of each pair ofelectrodes 420 and 422 receive electrical stimulation pulses at 1000Hertz within a certain distance from the respective pair of electrodes.FIG. 5A further depicts zones of stimulation 510A-510D, which representzones of tissue stimulation that may be affected by each of therespective pair of electrodes 420A-420D and 422A-422D. Zones ofstimulation 510A-510D may represent an electrical field (e.g., voltageor current propagation) or an activation field showing nerves activatedby the electrical field applied by the respective electrodes. Althoughzones of stimulation 510A-510D are shown as separate or not overlapping,two or more zones of stimulation 510A-510D may overlap in other examplesbased on the voltage or current amplitude, proximity of electrodes,tissue characteristics, or any other factors.

As described herein, a clinician may use an external programmer 104 toinstruct IMD 102 to deliver electrical pulse trains comprising aplurality of electrical stimulation therapy programs to a plurality oftissue sites of patient 12. By delivering a plurality of such electricalpulse trains to a plurality of tissue sites, IMD 102 may effectivelyprovide stimulation to large portions of spinal cord 20, thereforeensuring that at least some electrodes 116, 118 deliver electricalstimulation to a region of spinal cord 20 that effectively treat thecondition of patient 12.

In the example of FIG. 5B, electrodes 116, 118 are configured in asubstantially similar fashion to the electrodes depicted by userinterface 302 of FIG. 4 and as depicted in FIG. 5A. However, in theexample of FIG. 5B, IMD 102 has selected a different set of electrodepairs 116, 118 such that zones of stimulation 510A, 510B, 510E, and 510Fcover less tissue area than the zones of stimulation 510A-510B of FIG.5A. As described herein, IMD 102 may select different combinations ofelectrodes 116, 118 to test the different pairs of electrodes 116, 118for their efficacy in effectively treating the condition of patient 12.For example, as described herein, IMD 102 may remove combinations ofelectrodes 116, 118 that do not treat the condition of patient 12 so asto minimize energy consumption by IMD 102. As a further example, IMD 102may select different combinations of electrodes 116, 118 that generatezones of stimulation 510 to cover a small tissue area of patient 12(e.g., the electrode combinations are closer together) so as to reduceone or more side effects that occur with pairs of electrodes thatgenerate zones of stimulation 510 that cover a large tissue area ofpatient 12. Zones of stimulation 510A, 510B, 510E, and 510F mayrepresent an electrical field (e.g., voltage or current propagation) oran activation field showing nerves activated by the electrical fieldapplied by the respective electrodes. Although some zones of stimulation510A, 510B, 510E, and 510F are shown as overlapping, one or more (e.g.,all in some examples) zones of stimulation 510A, 510B, 510E, and 510Fmay not overlap each other (e.g., each zone covers distinct or separateareas of tissue) based on the voltage or current amplitude, proximity ofelectrodes, tissue characteristics, or any other factors. As discussedherein, for certainly pulse frequencies for example, it should be notedthat tissue subject to two or more zones of stimulation (e.g.,overlapping zones) may not respond differently than if the tissue wasonly subject to a single zone of stimulation. In such examples, thetissue (e.g., one or more nerves) receiving overlapping zones ofstimulation may not be affected by removal of one or more overlappingzones as long as the tissue is still subject to a single remaining zoneof stimulation.

FIG. 6 is a flowchart illustrating an example operation according to thetechniques of the disclosure. For convenience, FIG. 6 is described withrespect to IMD 102 of FIGS. 1 and 2. However, the techniques of FIG. 6may be performed different components of IMD 102 or by additional oralternative medical devices.

In the example of FIG. 6, IMD 102 delivers electrical stimulationtherapy according to a plurality of electrical stimulation therapyparameter sets to a plurality of tissue sites 14A-14D and 15A-15D ofpatient 12 (602). In one example, IMD 102 delivers electricalstimulation therapy according to each of the plurality of electricalstimulation therapy parameter sets via a respective combination of aplurality of electrodes 116, 118. In further examples, each combinationof electrodes comprises a pair of electrodes. In some examples, eachcombination of electrodes comprises at least two electrodes, includingone or more anodes and one or more cathodes.

The clinician determines whether the plurality of electrical stimulationtherapy parameter sets was effective in treating the condition ofpatient 12. This may occur during a trial period in which the IMD 102may be external from the patient or implanted. In some examples, thepatient provides feedback to the clinician that the plurality ofelectrical stimulation therapy parameter sets caused a reduction in apain sensation, In other examples, the clinician may determine whetherthe plurality of electrical stimulation therapy parameter sets waseffective by observing a bioelectrical response of patient 12, such as aresponse of a nerve or muscle tissue to the plurality of electricalstimulation therapy parameter sets. In some examples, the cliniciandetermines whether the plurality of electrical stimulation therapyparameter sets was effective during an implantation procedure where POD102 is implanted within patient 12.

In yet further examples, patient 12 provides feedback indicating thatthe plurality of electrical stimulation therapy parameter sets caused areduction in a pain sensation. For example, after delivering electricalstimulation therapy according to the plurality of electrical stimulationtherapy parameter sets, external programmer 104 provides, via userinterface 302, a prompt for patient 12 to provide the feedback. Inalternate examples, external programmer 104 may periodically (e.g., onceper day, once per week) provide the prompt to patient 12. Externalprogrammer 104 receives, via user interface 302, the feedback indicatingthe effectiveness of the plurality of electrical stimulation therapyparameter sets. In some examples, the patient feedback may be a painrating or estimation of pain relative to a pain scale. In some examples,external programmer 104 transmits the patient feedback to IMD 102.

In further examples, after delivering electrical stimulation therapyaccording to the plurality of electrical stimulation therapy parametersets, IMD 102 uses one or more accelerometers to determine that theplurality of electrical stimulation therapy parameter sets was effectivein treating the condition of patient 12. In still further examples,after delivering electrical stimulation therapy according to theplurality of electrical stimulation therapy parameter sets, IMD 102 mayuse data from the one or more accelerometers to evaluate functionalityof the patient, such as tremor, gait, flexibility, wrist flexion, orpatient movement, to determine whether the severity of the condition ofpatient 12 has improved or gotten worse.

Upon determining that the plurality of electrical stimulation therapyparameter sets was effective in treating the condition of patient 12,IMD 102 iteratively tests each of a plurality of subsets of theelectrical stimulation therapy parameter sets via a subset ofcombinations of electrodes 116, 118 to a subset of tissue sites 14A-14Dand 15A-15D of patient 12 (604). In some examples, IMD 102 performs suchiterative testing during a chronic period of time in which the patientis receiving therapy due to electrical stimulation therapy according tothe plurality of electrical stimulation therapy parameter sets beingeffective at treating the patient condition. For example, this chronicperiod may be post-trial and after implantation of IMD 102 withinpatient 12.

In some examples, as described above, for each of the plurality ofsubsets of the electrical stimulation therapy parameter sets, externalprogrammer 104 prompts patient 12 for feedback which of the plurality ofelectrical stimulation therapy parameter sets are effective in treatingthe condition of patient 12. In this example, external programmer 104receives such patient feedback and transmits the patient feedback to IMD102. IMD 102, based on the patient feedback, selects further subsets ofthe electrical stimulation therapy parameter sets for delivery of theelectrical stimulation. In alternate examples, IMD 102 compares theaccelerometer data for each of the plurality of electrical stimulationtherapy parameter sets in the manner described above to determine whichof the plurality of electrical stimulation therapy parameter sets areeffective in treating the condition of patient 12. For example, bydetecting an increased amount of activity by patient 12, IMD 102 maydetermine that patient 12 is suffering less pain (e.g., thereby allowingfor patient 12 to engage in more activity). As a contrasting example, bydetecting a decreased amount of activity by patient 12, IMD 102 maydetermine that patient 12 is suffering more pain (e.g., therebypreventing activity by patient 12). In this example, IMD 102, based onsuch accelerometer data, selects further subsets of the electricalstimulation therapy parameter sets for delivery of the electricalstimulation.

As one example, IMD 102 may deactivate at least one first combination ofplurality of electrodes 116, 118 (or deactivate a therapy programdefining the first combination of electrodes) such that at least onefirst electrical stimulation therapy parameter set of the plurality ofelectrical stimulation therapy parameter sets is not delivered topatient 12. IMD 102 may deliver electrical stimulation therapy accordingto the remaining electrical stimulation therapy parameter sets via theremaining combinations of electrodes 116, 118 and determine aneffectiveness of the remaining electrical stimulation therapy parametersets at treating the condition of patient 12. Further, IMD 102 mayreactivate the at least one first electrode combination of plurality ofelectrodes 116, 118 and deactivate at least one second electrodecombination of plurality of electrodes 116, 118. IMD 102 may deliverelectrical stimulation therapy according to the remaining electricalstimulation therapy parameter sets via the remaining combinations ofelectrodes 116, 118 and determine an effectiveness of the remainingelectrical stimulation therapy parameter sets at treating the conditionof patient 12. In this fashion, IMD 102 may test the effectiveness ofeach combination of electrodes 116, 118 in treating the condition ofpatient 12.

In another example, IMD 102 may deactivate one half of the combinationsof electrodes 116, 118 such that electrical stimulation therapy definedby a first half of the plurality of electrical stimulation therapyparameter sets is not delivered to patient 12. IMD 102 may deliverelectrical stimulation therapy according to the remaining electricalstimulation therapy parameter sets via the remaining combinations ofelectrodes 116, 118 and determine an effectiveness of the remainingelectrical stimulation therapy parameter sets at treating the conditionof patient 12. If the remaining electrical stimulation therapy parametersets are effective at treating the condition of patient 12, the firsthalf of the plurality of electrical stimulation therapy parameter setsmay not be necessary to provide therapy to patient 12, and may bedeactivated to conserve power. If the remaining electrical stimulationtherapy parameter sets are not effective at treating the condition ofpatient 12, then the first half of the plurality of electricalstimulation therapy parameter sets may be necessary to provide therapyto patient 12 and may be reactivated. Further, the remaining electricalstimulation therapy parameter sets may not be necessary to providetherapy to patient 12 and may be deactivated to conserve power.

Upon determining that at least one subset of electrical stimulationtherapy parameter sets treats the condition of patient 12, IMD 102selects at least one subset of electrical stimulation therapy parametersets for defining subsequent delivery of electrical stimulation topatient 12 (606) for chronic stimulation therapy. IMD 102 deactivatesthe combinations of electrodes 116, 118 that deliver electricalstimulation therapy determined not to he necessary for providing therapyto patient 112. Further, IMD 102 delivers electrical stimulation therapyaccording to the at least one subset of electrical stimulation therapyparameter sets to patient 12 via the respective combinations ofelectrodes 116, 118. In some examples, IMD 102 may perform such aniterative testing of the plurality of electrical stimulation therapyparameter sets on a periodic basis, such as daily, weekly, or monthly,so as to periodically determine a subset of electrical stimulationtherapy parameter sets that provides effective therapy to patient 12 butuses a minimal number of electrode combinations, and therefore a minimalamount of power.

FIG. 7 is a flowchart illustrating an example operation according to thetechniques of the disclosure. For convenience, FIG. 7 is described withrespect to IMD 102 of FIGS. 1 and 2. However, the techniques of FIG. 7may be performed different components of PAD 102 or by additional oralternative medical devices.

In the example of FIG. 7, IMD 102 delivers electrical stimulationaccording to a plurality of electrical stimulation therapy parametersets to a plurality of tissue sites 14A-14D and 15A-15D of patient 12,as described above with respect to 602 of FIG, 6. A clinician determineswhether the plurality of electrical stimulation therapy parameter setswas effective in treating the condition of patient 12 (702). In someexamples, the patient provides feedback to the clinician that theplurality of electrical stimulation therapy parameter sets caused areduction in a pain sensation. In other examples, the clinician maydetermine whether the plurality of electrical stimulation therapyparameter sets was effective by observing a bioelectrical response ofpatient 12, such as a response of a nerve or muscle tissue to theplurality of electrical stimulation therapy parameter sets. In someexamples, the clinician determines whether the plurality of electricalstimulation therapy parameter sets is effective during an implantationprocedure Where IMD 102 is implanted within patient 12. In yet furtherexamples, external programmer 104 receives, from patient 12, feedbackindicating that the plurality of electrical stimulation therapyparameter sets was effective. External programmer 104 transmits suchfeedback to IMD 102.

If the plurality of electrical stimulation therapy parameter sets doesnot treat the condition of patient 12 (e.g., “NO” block of 702), thenelectrical stimulation may not be effective in providing therapy topatient 12 (704). The clinician may attempt to try an alternativetherapy, such as different frequencies, amplitudes, or pulse widths, ortry implanting electrodes at different tissue sites. Otherwise, theclinician may determine that the patient does not respond to highfrequency electrical stimulation. However, if the plurality ofelectrical stimulation therapy parameter sets does treat the conditionof patient 12 (e.g., “YES” block of 702), then electrical stimulation iseffective in providing therapy to patient 12, and IMD 102 mayiteratively test different electrical stimulation therapy parameter setsso as to minimize the power usage of the system.

As one example, IMD 102 removes at least one of electrodes 116, 118 usedto deliver the electrical stimulation therapy according to the pluralityof electrical stimulation therapy parameter sets (706). In one example,IMD 102 removes a single one of electrodes 116, 118 (e.g., in amultipolar electrode configuration) or a single pair of electrodes 116,118 (e.g., in a bipolar electrode configuration) such that patient 12does not receive electrical stimulation therapy according to a singleelectrical stimulation therapy parameter set of the plurality ofelectrical stimulation therapy parameter sets. In an example bipolarconfiguration, a pair of electrodes includes two electrodes 116, 118. Inan example unipolar configuration, a pair of electrodes includes oneelectrode 116, 118 and a housing of IMD 102. Instead of removingelectrodes, IMD 102 may achieve the same result by removing one or moretherapy programs that define one or more electrode combinations. Inanother example, IMD 102 removes half of electrodes 116, 118 such thatpatient 12 does not receive electrical stimulation therapy defined byhalf of the plurality of electrical stimulation therapy parameter sets.IMD 102 delivers the electrical stimulation therapy according to theremaining electrical stimulation therapy parameter sets to tissue sites14A-14D and 15A-15D of patient 12 via the remaining electrodes 116, 118(708).

IMD 112 determines whether the remaining electrical stimulation therapyparameter sets treat the condition of patient 12 (710). If the remainingelectrical stimulation therapy parameter sets do not treat the conditionof patient 12. (e.g., “NO” block of 710), then IMD 102 restores theremoved at least one of electrodes 116, 118 (712) and removes at leastone different electrode of electrodes 116, 118 (712). It should be notedthat if removal of a single therapy program or single electrodecombination eliminates effective therapy for patient 12, IMD 102 mayidentify this change as that single therapy program or single electrodecombination as being responsible for effective therapy and proceed toblock 708 by delivering stimulation with only those electrodes that werepreviously removed and are likely responsible for effective therapy. IMD102 delivers electrical stimulation therapy according to the remainingelectrical stimulation therapy parameter sets (708) and determineswhether the remaining electrical stimulation therapy parameter setstreat the condition of patient 12 (710).

If the remaining electrical stimulation therapy parameter sets treat thecondition of patient 12 (e.g., “YES” block of 710), then IMD 102determines whether the remaining electrical stimulation therapyparameter sets are delivered via a single pair of electrodes 116, 118(714) (e.g., for a bipolar configuration, two electrodes 116, 118, andfor a unipolar combination, one of electrodes 116, 118 and a housing ofIMD 102). If IMD 102 is delivering electrical stimulation therapyaccording to the electrical stimulation therapy parameter sets via twoor more pairs of electrodes 116, 118 (e.g., “NO” block of 714), then IMD102 attempts to remove one of the pairs as discussed above. If IMD 102is delivering electrical stimulation therapy according to the electricalstimulation therapy parameter sets via a single pair of electrodes 116,118 (e.g., “YES” block of 714), then IMD 102 selects the remaining pairof electrodes 116, 118 for subsequent delivery of electrical stimulationtherapy according to a respective electrical stimulation therapyparameter set to patient 12. Although “pairs” of electrodes aredescribed with respect to the process of FIG. 7, IMD 102 may removeindividual electrodes or remove therapy programs that definecombinations of two or more electrodes.

FIG. 8 is a flowchart illustrating an example operation according to thetechniques of the disclosure. For convenience, FIG. 8 is described withrespect to IMD 102 of FIGS. 1 and 2. However, the techniques of FIG. 8may be performed different components of IMD 102 or by additional oralternative medical devices.

In the example of FIG. 8, IMD 102 delivers electrical stimulationtherapy according to a plurality of electrical stimulation therapyparameter sets to a plurality of tissue sites 14A-14D and 15A-15D ofpatient 12, as described above with respect to FIG. 6 (602). A cliniciandetermines whether or not the plurality of electrical stimulationtherapy parameter sets was effective in treating the condition ofpatient 12, as described with respect to blocks 702 and 704 of FIG. 7.

If the plurality of electrical stimulation therapy parameter sets treatthe condition of patient 12 (e.g., “YES” block of 702), then electricalstimulation is effective in providing therapy to patient 12, and IMD 102may iteratively test different electrical stimulation therapy parametersets so as to minimize the power usage of the system. For example, IMD102 selects one pair of electrodes 116, 118 of the plurality ofelectrodes 116, 118 (802). IMD 102 delivers electrical stimulationtherapy via the selected pair of electrodes 116, 118 to a respectivetarget tissue site of tissue sites 14A-14D and 15A-15D of patient 12(804). IMD 112 determines whether the delivered electrical stimulationtherapy treats the condition of patient 12 (806).

If the delivered electrical stimulation therapy does not treat thecondition of patient 12 (e.g., “NO” block of 710), then IMD 102 selectsa different pair of electrodes 116, 118 of the plurality of electrodes116, 118 (808). PAD 102 delivers electrical stimulation therapy via thedifferent pair of electrodes 116, 118 to a respective target tissue siteof tissue sites 14A-14D and 15A-15D of patient 12 (804). If thedelivered electrical stimulation therapy treats the condition of patient12 (e.g., “YES” block of 710), then IMD 102 uses the selected pair ofelectrodes 116, 118 of the plurality of electrodes 116, 118 forsubsequent delivery of electrical stimulation to patient 12 (810), Insome examples, if single electrode pairs do not maintain the effectivetherapy provided by the original plurality of electrical stimulationtherapy parameter sets, then IMD 102 may iteratively try two or moreelectrode pairs until a combination of electrodes is identified thatelicits the previously identified effective therapy.

While in this example, IMD 102 iteratively tests a single pair ofelectrodes 116, 118 of the plurality of combination of electrodes 116,118, in other examples, IMD 102 may iteratively test two or more pairsof electrodes 116, 118 or a group of three or more electrodes (e.g., agroup of three or more electrodes comprising at least one or more anodeelectrodes and one or more cathode electrodes). Upon determining asubset of two or more pairs of electrodes 116, 118 that effectivelytreats the condition of patient 12, IMD 102 may further test individualpairs of electrodes 116, 118 within the subset of two or more pairs ofelectrodes 116, 118 so as to further reduce the number of electrodes116, 118 that are used to effectively deliver electrical stimulation topatient 12.

The following examples illustrate one or more aspects of the disclosure.

EXAMPLE 1

A method comprising: delivering, by a medical device via a plurality ofelectrodes, a plurality of electrical stimulation therapies to aplurality of respective tissue sites of a patient, the plurality ofelectrical stimulation therapies treating a condition of the patient;subsequent to delivering the plurality of electrical stimulationtherapies, selecting a plurality of subsets of the plurality ofelectrical stimulation therapies, wherein each subset of the pluralityof electrical stimulation therapies includes at least one electricalstimulation therapy of the plurality of electrical stimulation therapiesand less than all of the plurality of electrical stimulation therapies,and wherein each subset of the plurality of electrical stimulationtherapies is delivered via a respective set of electrodes different fromsets of electrodes that deliver other subsets of the plurality ofelectrical stimulation therapies; iteratively delivering, by the medicaldevice, the subsets of the plurality of electrical stimulation therapiesto the patient via the respective sets of electrodes; and selecting atleast one subset of the plurality of electrical stimulation therapiesthat treat the condition of the patient for subsequent delivery to thepatient.

EXAMPLE 2

The method of example 1, further comprising delivering the selected atleast one subset of the plurality of electrical stimulation therapies tothe patient for a chronic period of time to treat the condition of thepatient, wherein the plurality of electrical stimulation therapies isdelivered for a trial period of time shorter than the chronic period oftime.

EXAMPLE 3

The method of any of examples 1-2, wherein iteratively delivering thesubsets of the plurality of electrical stimulation therapies via therespective sets of electrodes comprises iteratively delivering thesubsets of the plurality of electrical stimulation therapies via therespective sets of electrodes to a respective subset of the plurality ofrespective tissue sites, wherein each subset of the plurality ofrespective tissue sites does not include at least one tissue site of theplurality of respective tissue sites and is different from each othersubset of the plurality of respective tissue sites.

EXAMPLE 4

The method of any of examples 1-3, wherein each respective set ofelectrodes via which the subsets of the plurality of electricalstimulation therapies are delivered consists of a single cathode and asingle cathode.

EXAMPLE 5

The method of any of examples 1-4, wherein treating the condition of thepatient comprises reducing pain of the patient without substantiallyproducing paresthesia in the patient.

EXAMPLE 6

The method of any of examples 1-5, wherein the plurality of tissue sitesof the patient comprise at least a T9 vertebrae region of a spinal cordof the patient and a T10 vertebrae region of the spinal cord of thepatient.

EXAMPLE 7

The method of any of examples 1-6, wherein each electrical stimulationtherapy of the plurality of electrical stimulation therapies comprisesat least first electrical stimulation pulses at a first frequencygreater than about 600 Hertz and less than about 1,500 Hertz interleavedwith second electrical stimulation pulses at a second frequency greaterthan about 600 Hertz and less than about 1,500 Hertz to form a combinedpulse train with a combined pulse frequency of greater thanapproximately 1,500 Hertz.

EXAMPLE 8

The method of any of examples 1-6, wherein each electrical stimulationtherapy of the plurality of electrical stimulation therapies compriseselectrical stimulation pulses comprising a pulse frequency greater thanabout 600 Hz.

EXAMPLE 9

The method of any of examples 1-6, wherein each electrical stimulationtherapy of the plurality of electrical stimulation therapies compriseselectrical stimulation pulses comprising a pulse frequency greater thanabout 1000 Hz.

EXAMPLE 10

The method of any of examples 1-9, wherein selecting the plurality ofsubsets of the plurality of electrical stimulation therapies anditeratively delivering the subsets of the plurality of electricalstimulation therapies comprises iteratively: removing at least onesubset of the plurality of subsets of the plurality of electricalstimulation therapies; and delivering the remaining subsets of theplurality of electrical stimulation therapies to the patient via therespective sets of electrodes.

EXAMPLE 11

The method of any of examples 1-9, wherein selecting the plurality ofsubsets of the plurality of electrical stimulation therapies anditeratively delivering the subsets of the plurality of electricalstimulation therapies comprises iteratively: selecting at least onesubset of the plurality of subsets of the plurality of electricalstimulation therapies; and delivering the selected at least one subsetof the plurality of subsets of the plurality of electrical stimulationtherapies to the patient via the respective sets of electrodes.

EXAMPLE 12

The method of any of examples 1-11, wherein delivering the plurality ofelectrical stimulation therapies comprises delivering, by the medicaldevice, all electrical stimulation therapies of the plurality ofelectrical stimulation therapies substantially simultaneously with eachother.

EXAMPLE 13

The method of any of examples 1-11, wherein delivering the plurality ofelectrical stimulation therapies comprises delivering, by the medicaldevice, each electrical stimulation therapy of the plurality ofelectrical stimulation therapies on a time-interleaved basis with otherelectrical stimulation therapies of the plurality of electricalstimulation therapies.

EXAMPLE 14

The method of any of examples 1-13, wherein selecting the at least onesubset of the plurality of electrical stimulation therapies that treatthe condition of the patient for subsequent delivery to the patientcomprises selecting, based on feedback from the patient, the at leastone subset of the plurality of electrical stimulation therapies thattreat the condition of the patient for subsequent delivery to thepatient.

EXAMPLE 15

The method of any of examples 1-14, further comprising, generating, viaone or more accelerometers of the medical device and for each of thesubsets of the plurality of electrical stimulation therapies,accelerometer data indicating activity of the patient during delivery ofthe respective electrical stimulation therapies, wherein selecting theat least one subset of the plurality of electrical stimulation therapiesthat treat the condition of the patient for subsequent delivery to thepatient comprises selecting, based on the accelerometer data, the atleast one subset of the plurality of electrical stimulation therapiesthat treat the condition of the patient for subsequent delivery to thepatient.

EXAMPLE 16

A medical device system comprising: stimulation circuitry of a medicaldevice configured to deliver, via a plurality of electrodes, a pluralityof electrical stimulation therapies to a plurality of respective tissuesites of a patient, the plurality of electrical stimulation therapiestreating a condition of the patient; and processing circuitry configuredto: subsequent to delivering the plurality of electrical stimulationtherapies, select a plurality of subsets of the plurality of electricalstimulation therapies, wherein each subset of the plurality ofelectrical stimulation therapies includes at least one electricalstimulation therapy of the plurality of electrical stimulation therapiesand less than all of the plurality of electrical stimulation therapies,and wherein each subset of the plurality of electrical stimulationtherapies is delivered via a respective set of electrodes different fromsets of electrodes that deliver other subsets of the plurality ofelectrical stimulation therapies; iteratively control delivery, by thestimulation circuitry of the medical device, the subsets of theplurality of electrical stimulation therapies to the patient via therespective sets of electrodes; and select at least one subset of theplurality of electrical stimulation therapies that treat the conditionof the patient for subsequent delivery to the patient.

EXAMPLE 17

The medical device system of example 16, wherein the processingcircuitry is further configured to control delivery of the selected atleast one subset of the plurality of electrical stimulation therapies tothe patient for a chronic period of time to treat the condition of thepatient, wherein the processing circuitry controls delivery of theplurality of electrical stimulation therapies for a trial period of timeshorter than the chronic period of time.

EXAMPLE 18

The medical device system of any of examples 16-17, wherein, toiteratively control delivery of the subsets of the plurality ofelectrical stimulation therapies via the respective sets of electrodes,the processing circuitry is further configured to iteratively controldelivery of the subsets of the plurality of electrical stimulationtherapies via the respective sets of electrodes to a respective subsetof the plurality of respective tissue sites, wherein each subset of theplurality of respective tissue sites does not include at least onetissue site of the plurality of respective tissue sites and is differentfrom each other subset of the plurality of respective tissue sites.

EXAMPLE 19

The medical device system of any of examples 16-18, wherein eachrespective set of electrodes via which the subsets of the plurality ofelectrical stimulation therapies are delivered consists of a singlecathode and a single cathode.

EXAMPLE 20

The medical device system of any of examples 16-19, wherein, to treatthe condition of the patient, the selected at least one subset of theplurality of electrical stimulation therapies reduces pain of thepatient without substantially producing paresthesia in the patient.

EXAMPLE 21

The medical device system of any of examples 16-20, wherein theplurality of tissue sites of the patient comprise at least a T9vertebrae region of a spinal cord of the patient and a T10 vertebraeregion of the spinal cord of the patient.

EXAMPLE 22

The medical device system of any of examples 16-21, wherein eachelectrical stimulation therapy of the plurality of electricalstimulation therapies comprises at least first electrical stimulationpulses at a first frequency greater than about 600 Hertz and less thanabout 1,500 Hertz interleaved with second electrical stimulation pulsesat a second frequency greater than about 600 Hertz and less than about1,500 Hertz to form a combined pulse train with a combined pulsefrequency of greater than approximately 1,500 Hertz.

EXAMPLE 23

The medical device system of any of examples 16-21, wherein eachelectrical stimulation therapy of the plurality of electricalstimulation therapies comprises electrical stimulation pulses comprisinga pulse frequency greater than about 600 Hz.

EXAMPLE 24

The medical device system of any of examples 16-21, wherein eachelectrical stimulation therapy of the plurality of electricalstimulation therapies comprises electrical stimulation pulses comprisinga pulse frequency greater than about 1000 Hz.

EXAMPLE 25

The medical device system of any of examples 16-24, wherein, to selectthe plurality of subsets of the plurality of electrical stimulationtherapies and iteratively control delivery of the subsets of theplurality of electrical stimulation therapies, the processing circuitryis further configured to iteratively: remove at least one subset of theplurality of subsets of the plurality of electrical stimulationtherapies; and control delivery of the remaining subsets of theplurality of electrical stimulation therapies to the patient via therespective sets of electrodes.

EXAMPLE 26

The medical device system of any of examples 16-24, wherein, to selectthe plurality of subsets of the plurality of electrical stimulationtherapies and iteratively control delivery of the subsets of theplurality of electrical stimulation therapies, the processing circuitryis further configured to iteratively: select at least one subset of theplurality of subsets of the plurality of electrical stimulationtherapies; and control delivery of the selected at least one subset ofthe plurality of subsets of the plurality of electrical stimulationtherapies to the patient via the respective sets of electrodes.

EXAMPLE 27

The medical device system of any of examples 16-26, wherein, to controldelivery of the plurality of electrical stimulation therapies, theprocessing circuitry is further configured to control delivery of allelectrical stimulation therapies of the plurality of electricalstimulation therapies substantially simultaneously with each other.

EXAMPLE 28

The medical device system of any of examples 16-26, wherein, to controldelivery of the plurality of electrical stimulation therapies, theprocessing circuitry is further configured to control delivery of eachelectrical stimulation therapy of the plurality of electricalstimulation therapies on a time-interleaved basis with other electricalstimulation therapies of the plurality of electrical stimulationtherapies.

EXAMPLE 29

The medical device system of any of examples 16-28, wherein, to selectthe at least one subset of the plurality of electrical stimulationtherapies that treat the condition of the patient for subsequentdelivery to the patient, the processing circuitry is further configuredto select, based on feedback from the patient, the at least one subsetof the plurality of electrical stimulation therapies that treat thecondition of the patient for subsequent delivery to the patient.

EXAMPLE 30

The medical device system of any of examples 16-29, wherein the medicaldevice further comprises one or more accelerometers configured togenerate, for each of the subsets of the plurality of electricalstimulation therapies, accelerometer data indicating activity of thepatient during delivery of the respective electrical stimulationtherapies; and wherein, to select the at least one subset of theplurality of electrical stimulation therapies that treat the conditionof the patient for subsequent delivery to the patient, the processingcircuitry is further configured to select, based on the accelerometerdata, the at least one subset of the plurality of electrical stimulationtherapies that treat the condition of the patient for subsequentdelivery to the patient.

EXAMPLE 31

A medical device system comprising: means for delivering, via aplurality of electrodes, a plurality of electrical stimulation therapiesto a plurality of respective tissue sites of a patient, the plurality ofelectrical stimulation therapies treating a condition of the patient;means for, subsequent to delivering the plurality of electricalstimulation therapies, selecting a plurality of subsets of the pluralityof electrical stimulation therapies, wherein each subset of theplurality of electrical stimulation therapies includes at least oneelectrical stimulation therapy of the plurality of electricalstimulation therapies and less than all of the plurality of electricalstimulation therapies, and wherein each subset of the plurality ofelectrical stimulation therapies is delivered via a respective set ofelectrodes different from sets of electrodes that deliver other subsetsof the plurality of electrical stimulation therapies; means foriteratively delivering, by the medical device, the subsets of theplurality of electrical stimulation therapies to the patient via therespective sets of electrodes; and means for selecting at least onesubset of the plurality of electrical stimulation therapies that treatthe condition of the patient for subsequent delivery to the patient.

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware or any combination thereof. Forexample, various aspects of the described techniques may be implementedwithin one or more processors, including one or more microprocessors,digital signal processors (DSPs), application specific integratedcircuits (ASICs), field programmable gate arrays (FPGAs), or any otherequivalent integrated or discrete logic circuitry, as well as anycombinations of such components. The term “processor” or “processingcircuitry” may generally refer to any of the foregoing logic circuitry,alone or in combination with other logic circuitry, or any otherequivalent circuitry. A control unit comprising hardware may alsoperform one or more of the techniques of this disclosure.

Such hardware, software, and firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. In addition, any of thedescribed units, modules, circuits, or components may be implementedtogether or separately as discrete but interoperable logic devices.Depiction of different features as modules or units is intended tohighlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

The techniques described in this disclosure may also be embodied orencoded in a computer-readable medium, such as a computer-readablestorage medium, containing instructions. Instructions embedded orencoded in a computer-readable storage medium may cause a programmableprocessor, or other processor, to perform the method, e.g., when theinstructions are executed. Computer readable storage media may includerandom access memory (RAM), read only memory (ROM), programmable readonly memory (PROM), erasable programmable read only memory (EPROM),electronically erasable programmable read only memory (EEPROM), flashmemory, a hard disk, a CD-ROM, a floppy disk, a cassette, magneticmedia, optical media, or other computer readable media.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method comprising: delivering, by a medicaldevice via a plurality of electrodes, electrical stimulation therapyaccording to a plurality of therapy parameter sets to a plurality ofrespective tissue sites of a patient, the electrical stimulation therapytreating a condition of the patient, and wherein delivering theelectrical stimulation therapy according to the plurality of therapyparameter sets comprises one of: simultaneously delivering theelectrical stimulation therapy according to each therapy parameter setof the plurality of therapy parameter sets, or delivering the electricalstimulation therapy according to each therapy parameter set of theplurality of therapy parameter sets on a time-interleaved basis withother therapy parameter sets of the plurality of therapy parameter sets;subsequent to delivering the electrical stimulation therapy according tothe plurality of therapy parameter sets, selecting a plurality ofsubsets of the plurality of therapy parameter sets, wherein each subsetof the plurality of therapy parameter sets includes at least one therapyparameter set of the plurality of therapy parameter sets and less thanall of the plurality of therapy parameter sets, and wherein electricalstimulation therapy is delivered according to each subset of theplurality of therapy parameter sets via a respective set of electrodesdifferent from sets of electrodes that deliver other subsets of theplurality of therapy parameter sets; iteratively delivering, by themedical device, electrical stimulation therapy according to the subsetsof the plurality of therapy parameter sets to the patient via therespective sets of electrodes; receiving, for each of the subsets of theplurality of therapy parameter sets, feedback from the patientindicating whether the subset of the plurality of therapy parameter setstreated the condition of the patient; and selecting, based on thefeedback from the patient, at least one subset of the plurality oftherapy parameter sets that treat the condition of the patient fordefining subsequent delivery of electrical stimulation therapy to thepatient.
 2. The method of claim 1, wherein delivering electricalstimulation therapy according to the plurality of therapy parameter setscomprises delivering, by the medical device, electrical stimulationtherapy according to each therapy parameter set of the plurality oftherapy parameter sets on the time-interleaved basis with the othertherapy parameter set of the plurality of therapy parameter sets.
 3. Themethod of claim 2, wherein delivering electrical stimulation therapyaccording to each therapy parameter set of the plurality of therapyparameter sets on the time-interleaved basis with the other therapyparameter set of the plurality of therapy parameter comprises ceasingdelivery of all electrical stimulation therapy for a period of time ofabout 500 milliseconds between delivering electrical stimulation therapyaccording to each therapy parameter set of the plurality of therapyparameter sets.
 4. The method of claim 1, wherein iteratively deliveringelectrical stimulation therapy according to the subsets of the pluralityof therapy parameter sets via the respective sets of electrodes andreceiving feedback from the patient indicating whether each of thesubsets of the plurality of therapy parameter sets treated the conditionof the patient comprises: delivering electrical stimulation therapyaccording to a first subset of the plurality of therapy parameter sets;determining, based on the patient feedback, that the first subset of theof the plurality of therapy parameter sets does not treat the conditionof the patient; delivering electrical stimulation therapy according to asecond subset of the plurality of therapy parameter sets; anddetermining, based on the patient feedback, that the second subset ofthe of the plurality of therapy parameter sets treats the condition ofthe patient; and wherein selecting the at least one subset of theplurality of therapy parameter sets that treat the condition of thepatient for defining subsequent delivery of electrical stimulationtherapy to the patient comprises selecting the second subset of theplurality of therapy parameter sets for defining subsequent delivery ofelectrical stimulation therapy to the patient.
 5. The method of claim 1,wherein iteratively delivering electrical stimulation therapy accordingto the subsets of the plurality of therapy parameter sets via therespective sets of electrodes and receiving feedback from the patientindicating whether the subset of the plurality of therapy parameter setstreated the condition of the patient comprises: delivering electricalstimulation therapy according to a first subset of the plurality oftherapy parameter sets; determining, based on the patient feedback, thatthe first subset of the of the plurality of therapy parameter setstreats the condition of the patient; delivering electrical stimulationtherapy according to a second subset of the first subset of therapyparameter sets, wherein the second subset includes less than all of thetherapy parameter sets of the first subset; and determining, based onthe patient feedback, that the second subset of therapy parameter setstreats the condition of the patient; and wherein selecting the at leastone subset of the plurality of therapy parameter sets that treat thecondition of the patient for defining subsequent delivery of electricalstimulation therapy to the patient comprises selecting the second subsetof the plurality of therapy parameter sets for defining subsequentdelivery of electrical stimulation therapy to the patient.
 6. The methodof claim 1, further comprising delivering electrical stimulation therapyaccording to the selected at least one subset of the plurality oftherapy parameter sets to the patient for a chronic period of time totreat the condition of the patient, wherein electrical stimulationtherapy is delivered according to the plurality of therapy parametersets for a trial period of time shorter than the chronic period of time.7. The method of claim 1, wherein iteratively delivering electricalstimulation therapy according to the subsets of the plurality of therapyparameter sets via the respective sets of electrodes comprisesiteratively delivering electrical stimulation therapy according to thesubsets of the plurality of therapy parameter sets via the respectivesets of electrodes to a respective subset of the plurality of respectivetissue sites, wherein each subset of the plurality of respective tissuesites does not include at least one tissue site of the plurality ofrespective tissue sites and is different from each other subset of theplurality of respective tissue sites.
 8. The method of claim 1, whereinthe plurality of tissue sites of the patient comprise at least a T9vertebrae region of a spinal cord of the patient and a T10 vertebraeregion of the spinal cord of the patient.
 9. The method of claim 1,wherein each therapy parameter set of the plurality of therapy parametersets defines electrical stimulation therapy comprising at least firstelectrical stimulation pulses at a first frequency greater than about600 Hertz and less than about 1,500 Hertz interleaved with secondelectrical stimulation pulses at a second frequency greater than about600 Hertz and less than about 1,500 Hertz to form a pulse train with apulse frequency of greater than approximately 1,500 Hertz.
 10. Themethod of claim 1, wherein each therapy parameter set of the pluralityof therapy parameter sets defines electrical stimulation therapycomprising electrical stimulation pulses comprising a pulse frequencygreater than about 1000 Hz.
 11. The method of claim 1, furthercomprising, generating, via one or more accelerometers of the medicaldevice and for each of the subsets of the plurality of therapy parametersets, accelerometer data indicating activity of the patient duringdelivery of electrical stimulation according to the respective therapyparameter sets, wherein selecting the at least one subset of theplurality of therapy parameter sets that treat the condition of thepatient for defining subsequent delivery of electrical stimulationtherapy to the patient comprises selecting, based on the feedback fromthe patient and the accelerometer data, the at least one subset of theplurality of therapy parameter sets that treat the condition of thepatient for defining subsequent delivery of electrical stimulationtherapy to the patient.
 12. The method of claim 1, wherein deliveringthe electrical stimulation therapy according to the plurality of therapyparameter sets comprises simultaneously delivering the electricalstimulation therapy according to each therapy parameter set of theplurality of therapy parameter sets.
 13. A medical device systemcomprising: stimulation circuitry of a medical device configured todeliver, via a plurality of electrodes, electrical stimulation therapyaccording to a plurality of therapy parameter sets to a plurality ofrespective tissue sites of a patient, the electrical stimulation therapytreating a condition of the patient, and wherein the stimulationcircuitry is configured to deliver the electrical stimulation therapyaccording to the plurality of therapy parameter sets by one of:simultaneously delivering the electrical stimulation therapy accordingto each therapy parameter set of the plurality of therapy parametersets, or delivering the electrical stimulation therapy according to eachtherapy parameter set of the plurality of therapy parameter sets on atime-interleaved basis with other therapy parameter sets of theplurality of therapy parameter sets; and processing circuitry configuredto: subsequent to delivering electrical stimulation therapy according tothe plurality of therapy parameter sets, select a plurality of subsetsof the plurality of therapy parameter sets, wherein each subset of theplurality of therapy parameter sets includes at least one therapyparameter set of the plurality of therapy parameter sets and less thanall of the plurality of therapy parameter sets, and wherein electricalstimulation therapy is delivered according to each subset of theplurality of therapy parameter sets via a respective set of electrodesdifferent from sets of electrodes that deliver other subsets of theplurality of therapy parameter sets; iteratively control delivery, bythe stimulation circuitry of the medical device, of electricalstimulation therapy according to the subsets of the plurality of therapyparameter sets to the patient via the respective sets of electrodes;receive, for each of the subsets of the plurality of therapy parametersets, feedback from the patient indicating whether the subset of theplurality of therapy parameter sets treated the condition of thepatient; and select, based on the feedback from the patient, at leastone subset of the plurality of therapy parameter sets that treat thecondition of the patient for defining subsequent delivery of electricalstimulation therapy to the patient.
 14. The medical device system ofclaim 13, wherein the medical device further comprises one or moreaccelerometers configured to generate, for each of the subsets of theplurality of therapy parameter sets, accelerometer data indicatingactivity of the patient during delivery of electrical stimulationaccording to the respective therapy parameter sets; and wherein, toselect the at least one subset of the plurality of therapy parametersets that treat the condition of the patient for defining subsequentdelivery of electrical stimulation therapy to the patient, theprocessing circuitry is further configured to select, based on thefeedback from the patient and the accelerometer data, the at least onesubset of the plurality of therapy parameter sets that treat thecondition of the patient for defining subsequent delivery of electricalstimulation therapy to the patient.
 15. The medical device system ofclaim 14, wherein the processing circuitry is further configured tocease delivery of all electrical stimulation therapy for a period oftime of about 500 milliseconds between delivering electrical stimulationtherapy according to each therapy parameter set of the plurality oftherapy parameter sets.
 16. The medical device system of claim 13,wherein, to iteratively deliver electrical stimulation therapy accordingto the subsets of the plurality of therapy parameter sets via therespective sets of electrodes and receive feedback from the patientindicating whether each of the subsets of the plurality of therapyparameter sets treated the condition of the patient, the processingcircuitry is configured to: deliver electrical stimulation therapyaccording to a first subset of the plurality of therapy parameter sets;determine, based on the patient feedback, that the first subset of theof the plurality of therapy parameter sets does not treat the conditionof the patient; deliver electrical stimulation therapy according to asecond subset of the plurality of therapy parameter sets; and determine,based on the patient feedback, that the second subset of the of theplurality of therapy parameter sets treats the condition of the patient;and wherein, to select the at least one subset of the plurality oftherapy parameter sets that treat the condition of the patient fordefining subsequent delivery of electrical stimulation therapy to thepatient, the processing circuitry is configured to select the secondsubset of the plurality of therapy parameter sets for definingsubsequent delivery of electrical stimulation therapy to the patient.17. The medical device system of claim 13, wherein, to iterativelydeliver electrical stimulation therapy according to the subsets of theplurality of therapy parameter sets via the respective sets ofelectrodes and receive feedback from the patient indicating whether eachof the subsets of the plurality of therapy parameter sets treated thecondition of the patient, the processing circuitry is configured to:deliver electrical stimulation therapy according to a first subset ofthe plurality of therapy parameter sets; determine, based on the patientfeedback, that the first subset of the of the plurality of therapyparameter sets treats the condition of the patient; deliver electricalstimulation therapy according to a second subset of the first subset oftherapy parameter sets, wherein the second subset includes less than allof the therapy parameter sets of the first subset; and determine, basedon the patient feedback, that the second subset of therapy parametersets treats the condition of the patient; and wherein, to select the atleast one subset of the plurality of therapy parameter sets that treatthe condition of the patient for defining subsequent delivery ofelectrical stimulation therapy to the patient, the processing circuitryis configured to select the second subset of the plurality of therapyparameter sets for defining subsequent delivery of electricalstimulation therapy to the patient.
 18. The medical device system ofclaim 13, wherein the processing circuitry is further configured tocontrol delivery of electrical stimulation therapy according to theselected at least one subset of the plurality of therapy parameter setsto the patient for a chronic period of time to treat the condition ofthe patient, wherein the processing circuitry controls delivery of theelectrical stimulation therapy according to the plurality of therapyparameter sets for a trial period of time shorter than the chronicperiod of time.
 19. The medical device system of claim 13, wherein,after controlling delivery of electrical stimulation therapy accordingto the selected at least one subset of the plurality of therapyparameter sets to the patient for the chronic period of time, theprocessing circuitry is configured to: select a plurality of subsets ofa second plurality of therapy parameter sets, wherein each subset of thesecond plurality of therapy parameter sets includes at least one therapyparameter set of the second plurality of therapy parameter sets and lessthan all of the second plurality of therapy parameter sets, and whereinelectrical stimulation therapy is delivered according to each subset ofthe second plurality of therapy parameter sets via a respective set ofelectrodes different from sets of electrodes that deliver other subsetsof the second plurality of therapy parameter sets; iteratively controldelivery, by the stimulation circuitry of the medical device, ofelectrical stimulation therapy according to the subsets of the secondplurality of therapy parameter sets to the patient via the respectivesets of electrodes; receive, for each of the subsets of the secondplurality of therapy parameter sets, feedback from the patientindicating whether the subset of the second plurality of therapyparameter sets treated the condition of the patient; select, based onthe feedback from the patient, at least one subset of the secondplurality of therapy parameter sets that treat the condition of thepatient for defining subsequent delivery of electrical stimulationtherapy to the patient; and control delivery of electrical stimulationtherapy according to the selected at least one subset of the secondplurality of therapy parameter sets to the patient for the chronicperiod of time to treat the condition of the patient.
 20. The medicaldevice system of claim 13, wherein, to iteratively control delivery ofelectrical stimulation therapy according to the subsets of the pluralityof therapy parameter sets to the patient via the respective sets ofelectrodes, the processing circuitry is further configured toiteratively control delivery of electrical stimulation therapy accordingto the subsets of the plurality of therapy parameter sets via therespective sets of electrodes to a respective subset of the plurality ofrespective tissue sites, wherein each subset of the plurality ofrespective tissue sites does not include at least one tissue site of theplurality of respective tissue sites and is different from each othersubset of the plurality of respective tissue sites.
 21. The medicaldevice system of claim 13, wherein the plurality of tissue sites of thepatient comprise at least a T9 vertebrae region of a spinal cord of thepatient and a T10 vertebrae region of the spinal cord of the patient.22. The medical device system of claim 13, wherein each therapyparameter set of the plurality of therapy parameter sets defineselectrical stimulation therapy comprising at least first electricalstimulation pulses at a first frequency greater than about 600 Hertz andless than about 1,500 Hertz interleaved with second electricalstimulation pulses at a second frequency greater than about 600 Hertzand less than about 1,500 Hertz to form a pulse train with a pulsefrequency of greater than approximately 1,500 Hertz.
 23. The medicaldevice system of claim 13, wherein, to control delivery electricalstimulation therapy according to the plurality of therapy parametersets, the processing circuitry is further configured to control deliveryof electrical stimulation therapy according to each therapy parameterset of the plurality of therapy parameter sets on the time-interleavedbasis with the other therapy parameter set of the plurality of therapyparameter sets.
 24. A medical device system comprising: means fordelivering electrical stimulation therapy according to a plurality oftherapy parameter sets to a plurality of respective tissue sites of apatient, the electrical stimulation therapy treating a condition of thepatient, and wherein the means for delivering the electrical stimulationtherapy according to the plurality of therapy parameter sets comprisesmeans for one of: simultaneously delivering the electrical stimulationtherapy according to each therapy parameter set of the plurality oftherapy parameter sets, or delivering the electrical stimulation therapyaccording to each therapy parameter set of the plurality of therapyparameter sets on a time-interleaved basis with other therapy parametersets of the plurality of therapy parameter sets; means for, subsequentto delivering the electrical stimulation therapy according to theplurality of therapy parameter sets, selecting a plurality of subsets ofthe plurality of therapy parameter sets, wherein each subset of theplurality of therapy parameter sets includes at least one therapyparameter set of the plurality of therapy parameter sets and less thanall of the plurality of therapy parameter sets, and wherein electricalstimulation therapy is delivered according to each subset of theplurality of therapy parameter sets via a respective set of electrodesdifferent from sets of electrodes that deliver other subsets of theplurality of therapy parameter sets; means for iteratively deliveringelectrical stimulation therapy according to the subsets of the pluralityof therapy parameter sets to the patient via respective sets ofelectrodes; means for receiving, for each of the subsets of theplurality of therapy parameter sets, feedback from the patientindicating whether the subset of the plurality of therapy parameter setstreated the condition of the patient; and means for selecting, based onthe feedback from the patient, at least one subset of the plurality oftherapy parameter sets that treat the condition of the patient fordefining subsequent delivery of electrical stimulation therapy to thepatient.
 25. The medical device system of claim 13, wherein thestimulation circuitry of the medical device is configured to deliver theelectrical stimulation therapy according to the plurality of therapyparameter sets by simultaneously delivering the electrical stimulationtherapy according to each therapy parameter set of the plurality oftherapy parameter sets.